Chapter 4: Too Many Locked Rooms

That day, when Yozuki and I head headed to the dining room, B/breakfast wasn't ready yet.

“Maybe Ms. Breakfast overslept?”

Just as Yozuki tilted her head, Ms. Hitsujiko, face bloodless, ran in. “It's terrible!” she announced.

Ms. Hitsujiko explained that she'd been out on her morning walk when she saw fresh blood on the inside of the window of Poirotzaka's cottage. When she hurriedly went up the the window, she saw Poirotzaka was dead.

“Anyway, please come with me – Ahh, I have to go tell Lady Otomigawara as well!”

Ms. Hitsujiko ran off to call Otomigawara, and Yozuki and I decided to go ahead to Poirotzaka's cottage. As we hurried out of the mansion, we saw Ms. Chiyori and explained the situation to her as well.

Her face went pale for a moment, but she gathered her strength and said “Let's go,” then ran off towards the cottage. When we arrived at the cottage, we saw it.

The cottage where Poirotzaka was staying had a large south facing window, allowing us to clearly see inside. Poirotzaka was lying on the bed, and his head was lying on the floor. There was a massive amount of blood splattered around the room, making it obvious he'd been decapitated alive. And that wasn't even the strangest part.

The bed he was lying in had been placed in the center of the room.

And the bed had also been cut in two, tracing the cut of Poirotzaka's neck. It looked like a cut left by an overzealous chef on a thin, fragile cutting board. It was as though the culprit had broken into the cottage with a huge sword and swung it so forcefully that they not only lopped off Poirotzaka's head in one swing but also got the bed beneath him.

“Who the hell could have even done this?”

Ms. Chiyori looked stunned. The cut had thrown the bed out of alignment, and it now stood in the shape of a ku (く). She scratched her head from nerves and went around to the cottage's entrance. She put a hand on the doorknob, then grimaced.

“It's locked.”

In a way, that was predictable. I checked just to be sure, but the door actually was locked.

As we went back to the window to observe the scene again, I heard footsteps in the distance. When I looked over, I saw Ms. Hitsujiko and Otomigawara running towards us. Ms. Hitsujiko had a mop.

“Oh my stars!” Otomigawara announced excitedly, pressing her face to the window of the cottage. “It's a perfect recreation of one of Japan's Four Great Locked Rooms!”

Otomigawara, ever the locked room fanatic, couldn't hide her excitement. Perhaps she was inspired by her lady, for Ms. Hitsujiko's switch flipped, too.

“Yes... It's a wonderful locked room.”

Her eyes welled with tears. 

Goddammit, we didn't have time for this! I spoke to Otomigawara.

“Is it okay if I break the window?”

Otomigawara started, then nodded at me.

“It's fine, just do it.”

I took the mop from Ms. Hitsujiko and used it to shatter the glass. After making a hole large enough to admit entrance, we all entered the room.

As soon as I entered the cottage, I was assailed by a choking smell of rust. I got so dizzy I stumbled on my feet. Even Yozuki, who had strong nerves, grimaced at the amount of blood. But then she seemed to notice something and pointed, saying “Kasumi, look.”

Yozuki pointed at the cottage's west wall. There was a key hanging on a hook. Was it the key to this room? I went over and picked it up.

Then I turned my attention to the short passageway in the north wall of the cottage. At the end lay the entrance. There was a thumb turn on the inside of the door, which was set to the locked position. It was still locked.

I unlocked the door and stepped outside with Yozuki, shutting it behind us.

Then, I inserted the key I'd taken off the hook. I twisted it. The door locked. It was the real key. After unlocking the door and reentering the cottage, I saw an interior door. Inside was a washroom. Of course, there was no one inside. There were two more doors inside the washroom, revealing a bath and a toilet. As expected, no one was in there, either. It seemed unlikely that the culprit was still hiding inside the room. There weren't any other doors inside the cottage, so we returned to the main room where Poirotzaka's body was.

When I looked around the room again, I saw blood splatter on all four walls and the ceiling. It was horrible.

The interior walls of the room were all made of metal. No, not just metal... the entire cottage was made out of a special alloy. I remembered Ms. Hitsujiko had told me that earlier. The interior of the cottage had as silvery sheen, and the ceiling, floor, and walls were all engraved with a lattice pattern of ten centimeter squares, making it look like we were inside a giant Rubik's Cube. White lights were embedded in the four corners of the ceiling, highlighting the silver luster of the cottage and the vivid blood splatters.

“The key was real,” I informed everyone. “There aren't any others, are there?”

I asked Ms. Hitsujiko just to be sure, but she shook her head and said “Of course not. There is only one key to this cottage.”

“Then it's confirmed. It's a locked room.”

That was my conclusion. Ms. Chiyori heard that and muttered “I see,” in a dejected voice. It seemed she was taking it hard. But that was only natural. The fact that there had been another murder meant that Iori Yamazaki wasn't the culprit, and her reasoning had been wrong.

No, that wasn't necessarily true.

There was also the possibility that Dr. Iori had escaped her imprisonment and committed another murder. If she was the Living Locked Room Library and her work wasn't yet done, that was also a possibility. To confirm that...

“Let's head to the Tower of the Cross.”

The Tower of the Cross where Dr. Iori was imprisoned, and whether or not she was still there, was the key point here.

Otomigawara nodded at me.

“That is true. Ah, but first,”

She looked around the room. Her eyes landed on a travel bag placed against the west wall. Was it Poirotzaka's? Otomigawara unzipped the bag and looked inside. She let out a huff of satisfaction.

“Here it is.”

She took out a key. It was the key to the safe that Poirotzaka had kept. That safe held the key to the small room where the key to the Tower of the Cross was being kept. Without it, we couldn't enter the Tower of the Cross.

“Well, let's go.”

Otomigawara said that and we all left the room, her leading the way. But then I stopped. Something was bothering me. I was forgetting something important.

I turned back and looked under the bed where Poirotzaka was lying. A reached out to grab it. There was a toy rabbit in a tuxedo. It was still warm. As expected, the rabbit's head had been severed, just like Poirotzaka's, and both the head and torso were under the bed. And there was another miniature knife lying next to them. When I got the knife from under the bed, I saw the words “The Living Locked Room Library” engraved on the handle. I gulped.

As we thought, this was the work of the Living Locked Room Library – the killings hadn't stopped yet.

We went to Shitsugi's cottage to get the key to the Tower of the Cross. Ms. Hitsujiko took out the portable safe from the drawer in the wall.

“Let's unlock it.”

Otomigawara said that and inserted the key into the portable safe and turned it. The safe still wasn't unlocked. All five keys were needed to unlock it.

The remaining keys were being kept by Ms. Chiyori, Yozuki, Ms. Hitsujiko, and Poirotzaka. Poirotzaka's key had been recovered by Otomigawara from his bag earlier.

One by one, they unlocked the safe. When the safe was open, Ms. Hitsujiko got the key out of it. Key in hand, she went over to the door to the small room on the north side of the cottage and unlocked it.

On the back wall of the room, the key to the Tower of the Cross was hanging just like yesterday. Ms. Hitsujiko grabbed it and said “Let's head out.”

We nodded and headed out for the Tower of the Cross. But partway there, I had a sudden thought.

“Can we stop by the mansion for a moment? There's something I want to check.”

Everyone tilted their heads, but I ignored them and ran back to the mansion. When I arrived in the entrance hall, I saw exactly what I'd expected.

“The sword...” Ms. Hitsujiko said.

“It's gone!” exclaimed Otomigawara.

As they'd said, the great sword that was supposed to have been displayed in the mansion's entrance hall was missing. It was the sword Yozuki and I had seen when we first entered the mansion on Wire Mesh Island. If memory served, it was made out of a special alloy five times stronger than iron.

“So, the culprit used that sword to kill Poirotzaka,” said Ms. Chiyori. “Certainly, cutting through the entire bed to decapitate him was an unusual murder method. It probably wouldn't be possible without using that great sword.”

However, the great sword wasn't found in the cottage where the crime had taken place. Which meant the culprit was hiding it away for another purpose.

After leaving the mansion, we returned to the Tower of the Cross. When we reached the tower, Ms. Hitsujiko pressed the button to lower the room on the cross's right bar. When it landed on the ground, Ms. Hitsujiko unlocked the door with the key in her hand. And she opened the door.

We were all stunned.

Dr. Iori, who was supposed to have been confined there, wasn't in the room.

What was there was Gentleman, dead with a knife in his back.

“Impossible...” Ms. Chiyori said, completely dumbfounded. “What is Gentleman's body doing here?”

We all stared at the corpse, thinking the same thing as Ms. Chiyori. This wasn't possible. Because...

The key to the Tower of the Cross had been kept under flawless security, so there was no way for Dr. Iori to escape.

But we couldn't deny the reality before us. Not only had Dr. Iori disappeared, but Gentleman's corpse had been left in her place. It was like instant transmission. Dr. Iori and the old Gentleman – it was like they'd traveled through wormholes and swapped places.

“It's an impossible crime.”

Even Otomigawara, who loved locked rooms, was as dumbfounded as the rest of us. She was too confused to even enjoy herself.

A toy rabbit in a tuxedo was placed next to Gentleman's corpse. It had a miniature knife in its back, recreating the scene of Gentleman's death. And on the knife's handle was engraved a familiar name.”

“The Living Locked Room Library.”

I scratched my head. It appeared we'd made a huge mistake. I had though that the Living Locked Room Library was a locked room agent, but that was clearly a mistake.

The Living Locked Room Library was a monster.

I was sure they'd be remembered as one of the greatest locked room murderers of all time.

How could they not? If Dr. Iori were the Living Locked Room Library, then they would have had to have disappeared from this locked room like smoke. And if Dr. Iori weren't the Living Locked Room Library, that meant they had completely erased her, who was sealed in a locked room, from existence. And either way, there was the added bonus of somehow moving Gentleman's dead body into the locked room. I couldn't explain it – It may as well have been an act of God.

Such an undefeatable monster was hiding somewhere on Wire Mesh Island, planning to commit more locked room murders. We were completely helpless.

“Damn it!”

Ms. Chiyori let out an aggravated yell and ran to the only other room here, the washroom. She opened it, but of course, there was nobody there.

“Then, is it a secret passage?” Ms. Chiyori went to the wall and started tapping on it. “Is there a secret passage somewhere in this room that the Living Locked Room Library used to come and go?”

“Ms. Chiyori, please calm down!”

“How could I possibly stay calm!?”

After yelling that out, Ms. Chiyori grit her teeth with such force I worried they'd shatter. But I could understand her feelings. Looking at the situation, it was clear the Living Locked Room Library had her dancing in the palm of their hand.

“Anyway, we need to find Dr. Iori,” said Yozuki, immediately before she let out an “Eh?” “What's wrong?” I asked her.

“Nothing, it's just,” she said, frowning. “There's something I just noticed.”

“What is it?”

“Well...” Yozuki nodded with an apologetic look on her face. “I don't think I've seen Ms. Breakfast all day.”

Everyone in the Tower of the Cross went to Ms. Breakfast's cottage and looked in through the window, where we saw her dead with a knife in her chest. A toy rabbit in a dress was lying next to her. A miniature knife was in its chest, just like Ms. Breakfast's corpse. I couldn't really tell at that distance, but it looked like the knife's handle was engraved “The Living Locked Room Library.”

“...Another one.”

Ms. Chiyori sounded disgusted. The windows of the cottage were double hinged, but the crescent lock was taped in place. So I picked up a rock, broke the glass nearby, snapped a picture of the lock with my phone to preserve the evidence, removed the tape, and opened the window. We all entered the room and approached Ms. Breakfast's corpse.

She was dead, stabbed in the chest just like the rabbit. And there were two card keys lying next to her. Yozuki saw them and blinked.

“This room is locked with a key card, just like mine.”

Come to think of it, Yozuki's room was locked with a key card, just like mine. On the first day when we'd arrived on Wire Mesh Island, I'd been given two card keys by the now deceased Shitsugi.

I asked Ms. Hitsujiko about them.

“Are these two key cards the only ones to this cottage?”

“Yes, that's right,” Ms. Hitsujiko nodded. “This cottage has the same structure as the ones you and Ms. Yozuki are staying in. Like those, this one has only two key cards. There aren't any others, and there is no way to make a copy, either.”

“I see.”

I took another look at the two key cards on the floor. Then I turned my attention to the cottage's front door. The door had a thumb turn lock, and it was set to the locked position.

I picked up the two cards from the floor and unlocked the door. Yozuki followed me outside.

There was a card reader on the outside of the door. The reader was similar to the one on the cottage I was staying in, in that it didn't read the card on contact like a train IC card, but had to have the card inserted inside like a hotel room.

There was a plate with a 1 on it affixed to the door, and the key cards had 1s on stickers stuck to their surfaces. The numbers matched. However, it looked like it wouldn't be hard to remove and replace the stickers, so the culprit could have prepared a fake card in advance and stuck a sticker with a 1 on it. That meant there was a possibility that the culprit had left a fake key card to trick us into thinking the door was locked from the inside. Therefore, it was necessary to check whether the door could actually be locked by these two key cards.

I inserted the first key card into the card reader. There was a beeping sound, and the door locked. I pulled the doorknob just to check. It was locked properly.

“That means the first key card is real,” Yozuki said. “Now, if the second key card is also real...”

“The scene will be a locked room, and the situation is hopeless.”

“And yet, it is real, isn't it?”

Yozuki didn't mince words. Sighing, I inserted the second card into the reader. We heard the beep, and the door unlocked. Just like at my cottage, this door didn't have an autolock. When you inserted the key card into the reader, it locked, and when you inserted it again, it unlocked. To confirm, I inserted the second card into the reader again. As expected, the electronic beep sounded and the door locked. Then I took out the first card key and inserted it into the reader. The door unlocked.

That confirmed that the door could be locked and unlocked by either of the two key cards. Both key cards were real. And that meant the cottage was a complete locked room.

“Hey, can I try?”

Yozuki asked, and I handed her the key cards. Yozuki inserted them into the reader just like I had. Of course, the result was the same as before. Yozuki groaned.

“Welp, I'm out of ideas.”

That may have been, but there was still hope. There was still a small possibility that the culprit was hiding inside the room. So to confirm, I went back in through the front door and opened the door to the toilet. As expected, there was no one there. Feeling a bit silly, I opened the bathroom door. What I saw there shocked me.

“What's wrong, Kasumi – Wha!?”

Yozuki, who looked into the bathroom over my shoulder, was also surprised. But that was natural. Inside the bathroom...

For whatever reason, there was a coffin there.

It was a solid black coffin that looked like something Dracula would sleep in. Why was there a coffin in a place like this? Yozuki said something from behind me.

“...Is it Sotodomari's?” 

Honestly, the same thought had occurred to me.

But it was hard to imagine the self-proclaimed 1,000 year old vampire who camped out on the coast sleeping in a coffin in a place like this. As I was standing there being confused, I suddenly heard a loud bang from inside the coffin. Yozuki and I both shook. However, the coffin, unaware of our concerns, let out another bang. Then I heard a faint groan. Was...

“Is there someone inside that thing?”

Yozuki stared at the coffin. Then, as if it was threatening us, another bang sounded. Yozuki reflexively hid behind me and began to tug at my clothes.

“Hey, Kasumi, there's definitely someone in there.”

“Yeah, probably.”
When I looked at the coffin again, I saw a three digit combination lock on the outside of the lid. Staring at it, I spoke.

“Hey, Yozuki.”

“Huh? What?”

“Could you go open that lid?”

When she heard my request, Yozuki looked at me first in astonishment, than in contempt.

“Why me? Do it yourself.”

“What, because I'm a guy? That's pretty old fashioned. We live in an era of equality, you know?”

“That's not the sort of equality I want.”

“I thought you liked UMA.”

“Yeah, I like UMA! But the thing in that coffin definitely isn't a UMA!”

There was another bang from the coffin. We stepped back in fear.

“What's going on?”

Ms. Chiyori and the others heard the commotion and rushed into the bathroom. They were all surprised by the coffin.

Ms. Chiyori looked like she had a terrible headache.

“Hey, Kasumi, can I ask you something?”

“Sure, what is it?”

“Why is there a coffin in the bathroom?”

I didn't know that. Probably the only one who did was the person who'd put it there.

“Anyway, let's open the lid.”

Otomigawara announced that and approached the coffin. That was a brave woman. Or maybe it was that she didn't feel fear to begin with.

“A three digit combination?”

Otomigawara crouched next to the coffin and looked at the combination lock.

“Shall I fetch some wire cutters?” Ms. Hitsujiko asked, but Otomigawara shook her head and said no.

“If it's only three digits, it'll be faster to just brute force it. Give me a moment.”

Otomigawara started entering numbers, starting from 001. When she got to 036, the lock unlocked. Otomigawara turned to us.

“Well, let's open it.”

When everyone nodded at her, Otomigawara threw the coffin open. Its contents were revealed. For what felt like the hundredth time that day, we all received a shock.

Inside the coffin lay Dr. Iori, bound hand and foot. However, she wasn't a corpse. She was still alive. Her mouth was covered in duct tape, and she looked up at us with teary eyes, moaning through the tape.

Ms. Chiyori scratched her head.

“I just don't understand.”

We untied Dr. Iori and removed the duct tape placed over her mouth, then helped her out of the coffin. Otomigawara started the questioning.

“What were you doing in there?”

“I-I don't understand! I don't understand anything!” Dr. Iori said, tears overflowing and looking genuinely confused. “One moment, I was asleep in the Tower of the Cross, next thing I knew, I was trapped in a dark box... and I was in a coffin!”

“So, someone took you out of the Tower of the Cross.”

That, I could agree with. For example, if someone pumped sleeping gas into the room in the Tower of the Cross to make sure she stayed asleep, they could carry her to the the cottage and stuff her in the coffin without her realizing.

On the other hand, we could rule out the possibility that Dr. Iori was the Living Locked Room Library. Her hands and feet and clearly been tightly bound by someone else, and there was also no way she could have locked that combination lock on the outside of the coffin from the inside.

And besides which, she looked genuinely confused. But Otomigawara mercilessly forced even more confusing information on her. She laid out the incidents that had occurred on the island since that morning, when Poirotzaka, Gentleman, and Ms. Breakfast had all been found in locked rooms in quick succession.

As if to show off the impossibility, Yozuki showed her the two key cards to the cottage. Even she had been found in a locked room. When Dr. Iori realized that, she looked even more confused.

“And that's why I'd like to make a request, Iori.” Otomigawara didn't let up for a second. “I want you to perform autopsies on the three bodies and tell us their estimated times of death.”

Dr. Iori looked completely hopeless. Her face, already blue, turned paper white, and she looked around for a moment as though she were witnessing the end of the world. Then...

She vomited. And not just a little, either. Then she sprinted to the toilet and released the longest, loudest retches I'd ever heard in my life.

Eventually, she returned. Her complexion had gone beyond pale blue and become nearly translucent. Yozuki hurriedly stuffed the two key cards in her pocket and ran over to rub Dr. Iori's back. She looked back at Otomigawara with a hard face.

“Surely you see there's no way she can perform autopsies like this?”

Otomigawara sighed and eventually gave a nod.

“Nothing we can do. Let's just give up on the estimated times of death. The crimes were all committed last night, so probably nobody has an alibi anyway. By the way, Ms. Kurokawa, what do you plan to do now?”

Ms. Chiyori looked at her suspiciously. Raising an eyebrow, she asked,

“What do you mean?”

“Oh, it's nothing particularly deep,” Otomigawara shrugged. “It's just that your deduction that Iori was the culprit was completely wrong. That means your basis for suspecting her was also wrong. The locked room trick used on the basement door was wrong. In short, Ms. Kurokawa, you've been faced with a spectacular defeat. I was just wondering if you would bother investigating anymore.”

Ms. Chiyori glared daggers at Otomigawara.

But I couldn't exactly say she was wrong. When they were creating the locked room, the culprit poured water on the hinges of the door; with just that one action, they'd lead Ms. Chiyori to an incorrect conclusion, and as a result, Dr. Iori had been falsely accused. We'd all believed the case was solved, and that carelessness had given the culprit the chance to commit three more murders. In summary, Ms. Chiyori had completely fallen for a trap laid by the Living Locked Room Library. “Solving” the locked room and accusing Dr. Iori were all part of the script, and Ms. Chiyori was the lead actress. As Otomigawara said, she'd been completely defeated.

Ms. Chiyori seemed aware of that herself, as she looked like she'd swallowed an insect. Eventually, after choking back her anger, she spoke as calmly as she could make herself.

“Of course I'll continue the investigation. I won't lose again.”

Otomigawara grinned at her. And...

“Well then, I wish you the best. Don't worry, the Living Locked Room Library is definitely among us. I'm sure if the great genius Chiyori Kurokawa is on the case, I'm sure they'll be caught... eventually.”

With that mocking shot, she left the cottage. Ms. Hitsujiko followed after her.

After the two of them left, Ms. Chiyori grit her teeth and spoke.

“Aagh, I'm so frustrated,” she said, looking completely humiliated. “I've been made a complete fool of.”

“Well, I understand how you feel.”

“'Well, well', what is that, your Lt. Furuhata impression?”

“What? No!”

“I know that!”

She was angry! Unreasonably angry! Ms. Chiyori scratched her head.

“For now, let's just clear out these locked rooms already! Kasumi, come with me!”

Ms. Chiyori, nearly crying, stormed out of the cottage. Before I went after her, I called out to Yozuki, who hadn't moved from her spot.

“Um, what about you, Yozuki?”

“Go on without me,” she said. “I'm taking care of Dr. Iori.”

When I looked over, Dr. Iori was standing next to Yozuki, her complexion pale as ever. She no longer looked like she was dying. She may even have attained enlightenment.

And so Ms. Chiyori and I went to each locked room that had occurred up to now in turn. That is to say, the locked basement where Otozaki was killed, the Decapitation Chamber where Poirotzaka was killed, the locked Tower of the Cross where Gentleman was killed, and Ms. Breakfast's locked cottage.

After visiting each locked room, Ms. Chiyori grit her teeth.

“There are too many locked rooms here...”

I agreed. We'd spent time thoroughly investigating four different locked rooms, but we hadn't found a single clue.

“This isn't good,” Ms. Chiyori said, scratching her head. “These locked rooms are just too strong.”

The “strength” of a locked room refers to the difficulty in finding a way to solve it. Indeed, we couldn't make any progress in any of the locked rooms, so it could be inferred that their strength was quite high.

“It can't be helped,” Ms. Chiyori said irritably.

“I'm going to look at each scene again. We have to revisit each scene 100 times.”

“I don't think 'visiting the scene 100 times' is something that should be said so desperately.”

“I can't help it. I don't have any other ideas.”

Ms. Chiyori had lost all her confidence. There was no trace of the swagger she'd had solving the case yesterday. However, her desire to solve the case looked genuine.

There was nothing else to do. If that was how it was, than I had no choice but to use my last resort.

So I told her.

“Ms. Chiyori.”

“What?”

“I know how to solve these four locked rooms murders.”

Ms. Chiyori frowned at my words. Incredulously, she asked,

“Do you mean to tell me you managed to solve these locked rooms?”

I shook my head.

“No, I have no idea.”

When Ms. Chiyori heard me, she looked at me in confusion. And her voice sounded disappointed.

“What are you saying? Speak clearly, boy, I don't understand you.”

“It's simple,” I said. “I don't know how these locked rooms were made, and I definitely can't solve them myself. But I know how we can learn the solutions. Because there's someone on this island who can solve any locked room in an instant.”

Ms. Chiyori's eyes widened, and she quickly furrowed her brow. She knew what I meant, and she was revolted by the prospect.

“...No.”

She glared at me. I nodded back.

“Yes.” I said. “We need Shitsuri Mitsumura.”

Mitsumura had been “imprisoned” ever since her defeat on the first day of the Locked Room Trick Game. In actuality, her “prison” was a comfy room. Ms. Chiyori and I went to her “prison” and knocked on the door, and her voice answered.

“Come in.”

When I opened the door, I saw Shitsuri Mitsumura lying on the bed. She was still reading her paperback copy of Murder in the Silver Age of Locked Rooms.

“Oh, Kuzushiro,” Mitsumura said, getting up from the bed. “I heard about what happened. Sounds like things are pretty serious.”

When I looked at the claw-footed table next to the bed, I saw a half eaten Mont Blanc. It must have been brought by Ms. Hitsujiko. In that case, I wondered if Ms. Hitsujiko was the one who told her about all the havoc that had ensued that morning.

Either way, it simplified things for me. I asked “Mitsumura.”

“Help us solve this case.”

Mitsumura suddenly turned her back on me.

“Don't wanna. Sorry, but I refuse.”

“Huh? Why?”

“I'm busy reading Murder in the Silver Age.”

She probably meant Murder in the Silver Age of Locked Rooms. It was the only book in the room.

“And besides, you know,” she said. “I hate solving locked room mysteries.”

I couldn't repress a smile.

That was a blatant lie. There was nobody who loved locked room mysteries more than her.

But, well, all of her reactions thus far were expected. Mitsumura had a habit of reflexively rejecting any favor I asked of her. We probably should have had someone else ask, but it was too late for that now. I hadn't thought that far ahead.

But even if I'd made that mistake, there was no problem. Because wrangling this capricious princess was easy as one, two, three. One, I asked her. Two, she rejected me. And three, I poked her pride a bit. Observe:

“Welp, can't be helped. Let's go, Ms. Chiyori.”

“Huh? Wha – is that really okay?”

Ms. Chiyori was shocked I'd given up so easily.

“Yeah, it's fine. There's no point in relying on people with low abilities, anyway.”

I felt a surge of killing intent from behind me.

“When you say 'low ability', are you perchance referring to me?”

A low, sharp voice came from her. It was kinda scary. But I just shrugged my shoulders.

“I'm right, aren't I? You can't solve these locked rooms. That's why you're running away.”

When I said that, Mitsumura raised her eyebrows in suspicion.

“...I remember we've had this conversation before.”

“Have we, now?”

Come to think of it, I may have used similar tactics to get her in a helpful mood before. Seeing my reaction, Mitsumura narrowed her eyes at me.

“You're only pretending, aren't you? Don't you have any other way of manipulating me?”

So she knew I was manipulating her?

I thought about it for a moment.

“Well, this is the easiest way to handle you.”

“What do you mean, handle me? I'm not your henchwoman.”

“No, you aren't. You're my friend.”

“I don't remember being friends with you.”

Now that hurt. I always thought we were friends.

Seeing my reaction, Mitsumura hurriedly spoke again.

“Ah, sorry, that was too far. We are friends,” she blurted out. “But... I'm sorry. This is different.”

I slumped my shoulders.

“I'm sorry, too. I won't rely on you anymore.”

“Right...”

“Like I said, there's no point in relying on people with low abilities. Sorry, but we're busy. We don't have time for incompetents like you.”

Mitsumura slammed the paperback in her hands shut. Then she grabbed her pillow and threw it at me as hard as she could.

“Let's go,” Mitsumura said resolutely as she got up from the bed. “I'm going to show you just how high my abilities are.”

She dashed out of her “prison” in a blind rage. Seeing our exchange, Ms. Chiyori stared at me in shock.

“Is she always like that?”

“Oh, no, she's usually so much worse.”

“I see.”

She kept that shocked look on her face as she put the pillow Mitsumura had thrown at me back on the bed.

Ms. Chiyori and I first took Mitsumura to the place where Otozaki's body was discovered in the basement. There, we explained the details of the crime, the other locked rooms that had occurred thus far, and the turbulent developments we'd witnessed since that morning. Mitsumura nodded.

“So in other words, Ms. Kurokawa was miserably defeated.”

Ms. Chiyori looked annoyed.

“You're right, but it's annoying when you say it to my face like that.”

“Oh? I'm sorry, that was inconsiderate of me. But I'm a bit surprised. I didn't expect you to get so angry just from being told the truth. I suppose such petty adults do exist.”

There was no way she wasn't doing this on purpose. Hearing Mitsumura talk about her like she was worthless, Ms. Chiyori grit her teeth and seethed “So frustrating...” Then she asked me to intervene.

“Kasumi, this is so frustrating. There's no reason for her to be like this.”

I actually agreed with her.

“Why do you two keep fighting like this.”

“Because she looked at me like I was trash the whole trial.”

Mitsumura interrupted us and turned a disdainful gaze to Ms. Chiyori. Ms. Chiyori looked even more annoyed.

“You were the one who was looking at me like trash, weren't you?”

“Oh, really? I'm sorry, I didn't realize. But if there's an adult in front of you who looks like trash, you can't help how you look at them, you know?”

Mitsumura and Ms. Chiyori glared at each other for a while. Eventually, Mitsumura looked away and faced the basement door.

“I suppose it's time to start the investigation. I don't have so much free time that I can waste it dealing with immature adults.”

Ms. Chiyori grit her teeth again. After I calmed her down, I asked Mitsumura.

“Well? Any thoughts?”

“I think it might be a hinge trick after all. Since Dr. Iori isn't the culprit, the trick Ms. Kurokawa deduced must be wrong. However, I don't think she was that far off the mark. So if we just develop that idea a bit further...”

Mitsumura trailed off, looking at the hinge. “This hinge,” she said. “It's new.”

Hearing that, I turned my attention to the hinges fixing the door in place. They were shiny and did look like new.

I tilted my head.

“Were they replaced recently?”

“Hmm, I wonder. Shall we check the other rooms?”

Mitsumura ran over to the next door over in the hallway, opened it, and carefully checked its hinges.

“These are quite deteriorated.”

I looked at the hinges over her shoulder. It was true, the surface of the hinges were quite rough and looked like it had deteriorated. If you thought about it, that was a more natural appearance for a hinge.

However, that wasn't what the hinges of the basement door looked like. That meant...

“The people at the mansion replaced those hinges recently for some reason.”

Mitsumura let out a sigh.

“Kuzushiro, will you please use your brain a bit more?”

I thought I was using it plenty.

“Really? Do you even have a brain in there, or is it all kelp?”

“That is a weird question.”

“Well... I think I won't be eating kelp any time soon.”

Even though Mitsumura was the one who'd brought it up, she looked a bit uncomfortable.

“In other words,” said Ms. Chiyori, “You're saying the fact that he door hinges were replaced means that it was the culprit's doing?”

Mitsumura grinned.

“That's right. And the fact that the culprit replaced the hinges means that a hinge trick was used after all. Just a different one than Ms. Kurokawa's.”

That was a sensible conclusion, but it was also wrong. Because,

“The trick Ms. Chiyori came up with was, in short, that the screws of the hinges weren't replaced until after the locked room was broken down,” I said. “But if that trick wasn't used, then that means the screws were already in place when the culprit locked the room. But that's absolutely impossible, right? Because that door... When it's closed, the screw holes on the hinges are caught in between the door and the frame. There's no way to apply the screws while the door is in place, right?”

Mitsumura nodded at me. “That's true.”

With that, she walked back down the hall to the basement door. Then she looked back at the hinges holding the door in place.

“Kuzushiro?”

“Yes?”

“How much of your life have you dedicated to thinking about hinges?”

I was suddenly asked a mysterious question. I was probably the first person in history to be asked that.

“Hmm,” I thought for a moment.

“Probably about 30 minutes.”

“I'd say about two hours,” said Ms. Chiyori.

“That isn't much,” Mitsumura said in shock. “I've spent about 500 hours.”

That is too much! You are weird!

“So I know a fair amount about the structure of a door hinge,” Mitsumura said with cool eyes. “So, to be honest, I knew what sort of trick the culprit used right away.”

She knew what sort of trick the culprit used... Ms. Chiyori and I were both rooted to the floor.

“Is that true?” I asked, and Mitsumura cleared her throat.

“First, allow me to explain the structure of a hinge.”

She held up her index finger.

“A hinge is primarily composed of four parts: two metal plates, a pin, and a cap to hold the pin in place. The two metal plates move in opposite directions, and when they're pressed together, the joint connecting them forms a cylindrical shape. The pin is inserted into this cylinder and covered by the cap. That allows the two metal plates to rotate on the pin's axis.”

As I listened to her explanation, I tried to visualize a typical hinge in my mind. They're called butterfly hinges because their shape resembles a butterfly. The two metal plates flapped like the wings, and the pin was the body.

“By the way, the pin is generally shaped like a nail with a blunted tip,” Mitsumura said. “And the cap is the shape of the pin's head. In other words, when the pin and cap are attached, it resembles a dumbbell – a metal bar with a disc at each end. The pin and cap are usually held together by pressure. A machine presses them together with great force until they are fused.”

Mitsumura stroked her black hair.

“Here's the important bit: Why did the culprit replace the hinge with a brand new one? What's important is why it was brand new. Allow me to explain. As I said, a hinge has four parts: Two metal plates, pin, and cap. The hinge is completed when the four parts are assembled at the factory. So, I considered the possibility that the culprit used unfinished hinges, ones that hadn't yet been assembled at the factory.”

They used unfinished hinges? When I tilted my head at her, Mitsumura said “That's right.”

“The culprit removed the old hinges from the door and the door frame and replaced them with unassembled hinges. The only things screwed to the door and frame were the two metal plates. With the door in that state, they turned the thumb turn to extend the deadbolt and inserted the door back into the frame. However, this door opens inwards, so it would be quite difficult for someone on the hallway side to fit it snugly into the frame. When fitting a door that opens inwards, it's necessary to push the door from the inside of the room towards the hallway side, because the door frame itself is the only thing catching the door in place. This is where the special adhesive that dissolves in hot water made by Otomigawara Industries comes in. By attaching additional catches to the outside door with the adhesive, the door could be more easily installed from the hallway side. Now, the culprit had succeeded in fitting the door in the frame. But what was the state of the hinges at that point? The two metal plates were shaped to fit each other, so when the door was closed, they should naturally be pressed together. But they were only being pressed together. The metal plates were not yet fixed, because there was no pin inserted into the point where they met – that is, the cylinder. In other words, if someone pressed on the door and applied force to the hinges, the two metal plates would come apart, and when the door was re-fitted, they would come back together. It was a precarious situation, hardly worthy of the name 'locked room'.”

 

“So, in order to make it a locked room, they had to insert the pins back into the hinges,” said Ms. Chiyori. “But how did they do that? When the door was fitted into the frame, the culprit must have been on the hallway side. If that were the case, there'd be no way for them to insert the pin, right? Because the door opens inwards.”

Ms. Chiyori had it right. The cylindrical part where the pin was inserted, created by the contact between the two metal plates, was on the outside of outward opening doors, and the inside of inward opening doors. Since the door rotated on that cylindrical structure, that had to be true. Since this was an inward opening door, there was no way to insert the pin from outside the room.

“Indeed, Ms. Kurokawa is correct,” Mitsumura admit. “As you said, it isn't possible to insert the pins into the hinges normally, so some creativity is required. I'm afraid we have no choice but to once again use the forbidden cheat item.”

Ms. Chiyori and I exchanged a look. Eventually, I tilted my head and asked “Forbidden cheat item?”

“Yes,” Mitsumura nodded. “Liquid nitrogen.”

“They used liquid nitrogen?”

Ms. Chiyori and I were both turning into parrots. This was the exact same substance used in the locked cottage trick where Shitsugi was killed. So, the culprit used liquid nitrogen to create locked rooms.

“So, how did they use the liquid nitrogen?”

To be honest, even knowing that liquid nitrogen was the answer, I had no idea how they could have inserted the pin.

“It's easy,” Mitsumura said. “The culprit had previously inserted the pin shallowly into the cylindrical part of the metal plate on the hinge. They dropped it in the top like a pen in a pen holder. Then, they slightly wet the pin and froze it in place with liquid nitrogen. If they did that, it would remain where it was above the cylinder, right? With it like that, they fitted the door in place from the corridor side. At that point, the two metal plates of the hinge were connected for the first time, with the pin shallowly inside the cylinder – only the tip, fixed in place with ice. Because the pin was so shallow, it didn't get in the way when the metal plates were joined. If it were deeper, it would have blocked them. With the hinges together, the pin was hovering above the cylinder, affixed by ice. So, what happens when the ice melts? It's obvious, isn't it? When the ice melts, the pin is affected by gravity and falls into the cylinder. In other words, when the ice melts, the pin inserts itself.”

I pictured the scene in my head. When the ice melted, the pin fell into the cylindrical part of the hinge. That meant the culprit could insert the pin into the cylinder on the inside from out in the hall.

“Then, by inserting the pin, the two metal plates making up the hinge were held in place together,” Mitsumura said. “At that point, the pin still wasn't attached to its partner, the cap. Although it sounds unstable, it actually held together quite firmly. At least, if pushed horizontally... Even if the door was pushed from the hallway side, since the pin was inserted between the two metal plates, it held them together and they didn't come apart. If you wanted to take the hinge apart, all you had to do was pull out the pin, but unless that was done, the hinge wouldn't come apart.”

I was surprised.

“So when the body was discovered, the pin wasn't fused with the cap, but simply inserted into the cylinder?”

“Yes, that's how it was,” Mitsumura nodded. “By the way, the cap was glued to the hinge with the hot water adhesive. If they did that, it would look like a complete hinge. All that was left was to break down the door and reveal the corpse. After the body was discovered, maybe that evening, the adhesive was melted, the cap removed, and a portable machine was used to fuse the pin and cap, building the hinge on the spot. That way, the investigation would find the door and the frame connected by proper hinges.”

Seeing us both staring at her with jaws hanging open, Mitsumura spoke again.

“This is the truth of the locked room trick.”

We were taken aback. It had been less than ten minutes since Mitsumura had started her investigation. And yet, she had already broken one of the locked rooms.

“You...” Ms. Chiyori said in disbelief. “Why did you use a trick like that in the Locked Room Trick Game if you could imagine things like this? You could have come up with something far better.”

Mitsumura looked a bit displeased. “I'll have you know I'm quite proud of that trick. I don't appreciate your criticism.”

 

“I also may have underestimated Ms. Kurokawa a bit too much. I thought for sure... that a trick of that level would be enough to defeat you.”

Mitsumura pouted a bit. Apparently, losing the game so easily was a stain on her honor. She looked upset with herself.

“At any rate, the locked basement murder is now resolved,” Mitsumura said, “and this trick could have been performed by almost anyone other than Dr. Iori. So let's just move on. There are three locked rooms remaining, and I'd like to get them all over and done with today.”

Next we went to the scene of Poirotzaka's murder, the famous Decapitation Chamber. Poirotzaka's body (and head) had already been taken to the wine cellar, but the scene was still gruesomely splattered in blood.

Mitsumura entered the scene, looked around, and said coolly,

“Oh, this is awful.”

The way she said that made me question if she really meant it. While Ms. Chiyori and I looked at her suspiciously, Mitsumura searched the room, then said “Over there”, pointing to the bed in the center of the room.

“Mr. Poirotzaka was killed over there, wasn't he?”

I nodded. Poirotzaka had been decapitated while lying in bed. The bed had been cut along the same line as his neck. In other words, the culprit had decapitated not only Poirotzaka, but his bed.

“Hmm, that's impressive,” Mitsumura said casually. “By the way, what was the murder weapon? How was he decapitated?”

I gave Mitsumura an outline of the case, but I must have forgotten to tell her about the murder weapon. I explained that now.

“Hmm, so it was the great sword displayed in the entrance hall,” Mitsumura said. “I saw that sword the day I arrived on the island. I believe it had a blade of about 3 meters.”

“Yeah, that sword looked like something out of a fantasy anime. If they swung it as hard as they could, it could easily cut through a man's neck.”

“But why did they cut the bed?”

“Huh?”

“And this bed is fixed to the floor.”

Mitsumura bent down next to the bed and indicated. Looking again, the bed was indeed fixed to the floor with screws. It didn't look like the culprit's doing; I'm pretty sure it was built like that. But did that matter at all?

“Hmm.”

Mitsumura was still thinking as she stood up from beside the bed and moved over to the wall. The metal walls were made of the special alloy. There was a lattice pattern engraved on the walls. To be specific, it wasn't just on the walls, but also the floor and ceiling.

Mitsumura knocked on the wall.

“It doesn't seem possibly to make a hole in a wall like this.”

So there was no possibility that they punched a hole in the wall and used it in a trick.

“Let's investigate the outside of the cottage.”

Without waiting for a response, she stepped outside. Ms. Chiyori and I followed her.

Looking at the cottage from the outside, it was just a metal box. A rectangular metal building with a cubic protrusion containing the entrance and a bathroom. Poirotzaka's body had been found in the rectangular section. The rectangular building had north and south walls measuring 6 meters long, and east and west walls measuring 3 meters long. And the building was 2 meters tall. There was a large fixed window on the south wall, which we'd broken to get into the room upon finding the body.

Mitsumura circled the cottage. The cottage was located about 10 meters from the road, and it was surrounded by nothing but empty land. Mitsumura stopped in front of the east wall and knocked on it. Then she tilted her head to the side as though she'd noticed something wrong, took a few steps back, and threw herself against the wall.

Ms. Chiyori and I were both startled. Ignoring us, Mitsumura tackled the wall again, recoiling in pain and looking dizzy.

“My head hurts...”

Well, yes. You'd just body tackled a metal wall.

“What are you doing?” Ms. Chiyori reprimanded.

“It's this wall,” Mitsumura said. “It feels like if you push it hard enough, it will tilt inwards.”

Ms. Chiyori looked at her dubiously.

“The wall tilts? What do you mean?”

“Exactly what I said. It tilts. This east wall can be tilted into the room.”

I frowned at her and tried pushing the wall with both hands. When it didn't budge, I put all my weight on the wall. I thought I felt it tilting into the room. But honestly, I wasn't sure.

“It feels like it can tilt, but it also feels like it can't.”

Which one was it?

Seeing me like that, Mitsumura said “We'll need to do some testing.” Then she gave me an order.

“I'll need some help. Bring over Yozuki and... yes, Ms. Hitsujiko.”

Following Mitsumura's instructions, I called Yozuki and Ms. Hitsujiko over to the cottage.

“What should we do?”

When Yozuki arrived and asked that question, Mitsumura replied “Good, you knew to ask.”

“Yozuki, you're in charge of hitting the wall.”

“In charge of hitting the wall?” Yozuki looked confused. “Is that a job?”

“It is now.”

“Hmm. Well, then, it can't be helped. I humbly accept this new responsibility.”

Yozuki accepted her new role as person in charge of hitting walls. She was a flexible woman. I really respected that about her.

“Now, everyone, please stand in front of this wall.”

At Mitsumura's order, Ms. Chiyori, Yozuki, Ms. Hitsujiko, and I all lined up in a row facing the wall. And Mitsumura gave the order.

“Everyone, hit that wall as hard as you can.”

That was probably the first time in history anyone had ever given that order. We on wall hitting duty followed our orders and rammed the wall with great force. My head spun from the impact. As we all lay there, writhing in agony, Mitsumura spoke happily.

“Ah, it did tilt a bit. In other words, this wall is designed to tilt inwards into the cottage.”

Then she suddenly put on a thoughtful look and turned back to us.

“But the tilt was so small I'm not sure I really saw it. Just to be sure, let's all hit it again.”

It was a cruel order that showed no consideration for her fellow man. Naturally, I objected.

“No, it's okay, really. The wall definitely tilted. I felt it.”

When I hit the wall, I felt it tilt. I definitely felt it. Certainly. I am not just saying this because I didn't want to hit the wall again.

As if she understood my thoughts, Mitsumura gave a gentle nod.

“Alright, If Kuzushiro says so, I'll believe it.”

“Thank you.”

“Ah, but...” Mitsumura said awkwardly. “There are three other walls, right? It is a rectangular building.”

“............”

“So I'm sorry, but would you please hit the other walls, too?”

After we'd thrown ourselves against all four walls of the cottage, it was determined that only the east wall tilted. Apparently, the other walls weren't built to move.

“Hmm, interesting. So only the wall on the east side tilts?” Mitsumura said with clear interest.

“But that means... What?” That's when I realized. “If the wall tilts, then doesn't that mean if it were tilted even further, there would be a gap between the wall and the ceiling? Maybe that's how the culprit got in and out.”

In other words, knocking over the wall could create a secret passage.

But Mitsumura shook her head and said “I'm afraid that isn't the case.”

“According to the results of our current wall hitting experiments, the east wall and the ceiling are firmly connected. So no matter how far the east wall tilts, there will be no gap between the wall and ceiling. Conversely, the east and south walls aren't connected. So even if the east wall were to completely collapse, the south wall wouldn't move. The same goes for the east and north walls. When the east wall moves, the north remains in place.”

I pictured it in my head. Even though the east wall tilted, the walls on either side of it remained in place.

As I pictured the scene, Mitsumura looked up at the cottage's roof.

“Ms. Hitsujiko.”

“Yes?”

“I'd like to climb up on the roof of the cottage, are there any ladders or things like that? Also, I need something round. A ping pong ball, a pachinko ball, something of that nature.”

Ms. Hitsujiko gave a strange look at the request, but acquiesced.

“If a ping pong ball is acceptable, I'm sure I can find one. I'll go get it for you now.”

With that, Ms. Hitsujiko headed off towards the mansion. About ten minutes later, she returned with a stepladder and a ping pong ball. Mitsumura thanked her and climbed up on the roof of the cottage. Curious what she was doing, I climbed after her.

“Why on Earth did you come up here?” I asked.

“Because there's something I'd like to find out.”

Mitsumura bent down on the roof and took the ping pong ball out of her pocket. The cottage was built in the shape of a rectangle, so the roof was flat and rectangular. There was a lattice pattern carved on it, just like the interior walls.

Mitsumura gently placed the ping pong ball on the roof. It started rolling, even though she hadn't touched it. There was no wind, either. Did that mean the roof was slanted?

Eventually, the ping pong ball stopped about a meter from the center of the roof. Mitsumura nodded.

“As expected, it seems the roof is slanted.”

The roof did appear to be slanted, but what did “as expected” mean? What basis did she have for thinking the roof was at an angle?

But Mitsumura didn't see fit to explain herself and climbed the stepladder back down from the roof of the cottage. Then she turned to Ms. Hitsujiko.

“Ms. Hitsujiko, would you please show me around the island? There's something I'd like to know.”

“Of course, I don't mind.”

Ms. Hitsujiko and Mitsumura were about to leave the cottage. Then, as if she'd had a sudden idea, Mitsumura stopped and turned back.

“Kuzushiro, would you like to come, too?”

“Well, sure.”

“And will Ms. Kurokawa be coming as well?”

“Well, sure.”

“Um, Mitsumura, what about me?”

“Of course you can come too, Yozuki.”

In the end, everyone there decided to join Mitsumura on her walk around the island. However, even after going around the island, we didn't find anything I didn't already know.

But when we finished our walk, Mitsumura made an announcement.

“The mystery is solved. I know how the culprit was able to lock this room.”

Mitsumura ordered us back to the cottage where the murder had taken place, so Yozuki and I went back and waited for her. Ms. Hitsujiko had work to do back at the mansion, so she left us and went off somewhere. And Ms. Chiyori was nowhere in sight. She had been whispering with Mitsumura earlier, so maybe she was going to help recreate the trick. I really didn't know if those two got along or not.

As I stood thinking things like that, Mitsumura eventually appeared. I don't know where she got it from, but she was holding a life-sized French doll. It was a large doll with thick golden hair, and it was, frankly, creepy. Mitsumura placed the doll where Poirotzaka's corpse had been, that is, on the bed chopped in two. After leaving the cottage, she took up position in front of the south wall, near the large window.

“Well, let's begin the deduction.”

Mitsumura stroked her long black hair.

“Now, the key aspect of this locked room is the east wall of the cottage. As we just determined, it leans towards the interior of the cottage. Since the walls of ordinary buildings don't tilt, it is obvious this wall was designed to tilt on purpose. There must be a joint between the wall and the floor. And here is the important part: Of the four walls of the cottage, only the east wall is made to tilt. That means the other walls weren't built to tilt. But that obviously can't be, right? It's completely contradictory.”

Yozuki and I looked at each other. Completely contradictory... That's what Mitsumura said, but I had no idea what she meant.

Seeing we didn't understand, Mitsumura sighed.

“It seems I overestimated Kuzushiro. No, I knew your intelligence was low, but it seems I still thought too highly of you. It's completely my fault. I'm sorry I expected anything of you. I should have tailored the conversation to your level.”

I grit my teeth. Did she have to say all that just because I didn't understand one thing? Her personality really was terrible. No, I knew her personality was bad, but it seemed I still thought too highly of her. It was completely my fault. I should have tailored the conversation to her bad personality.

So I resisted the urge to complain and flattered her.

“Please enlighten me, Ms. Mitsumura.”

“It can't be helped,” she sighed. Be patient. Be the adult. Be patient.

“Think about it like this,” Mitsumura said. “The cottage is a rectangle, right? So if one wall tilted inwards, in would be strange if the other walls didn't do so as well. Otherwise, the cottage itself would fall apart. It would be strange if the east wall tilting didn't also tilt the west wall the same amount. Remember when we learned about parallelograms in elementary school. When the right side of a rectangle tilts, the other side also tilts at the same angle. Otherwise, the figure can't maintain balance and falls apart. When we checked the walls of the cottage earlier, the east wall could move, but the west wall didn't. This is a contradiction. So, does anyone have any ideas on how to solve this contradiction?”

Yozuki and I looked at each other again. “For the moment, let's draw it out,” Yozuki said, squatting down and sketching a diagram in the dirt with a stick. After drawing a few diagrams of rectangles and parallelograms, she said “I don't get it. To begin with, it's been a while since I last heard the word 'parallelogram'. What even is that? Is it like a trapezoid?” Was a parallelogram like a trapezoid? It was a complicated question.

Mitsumura looked at us and shrugged, then took something out of her pocket and handed it to us, saying “It can't be helped, use this.” It was origami... We really were back in math class. Moreover, it was grade school math class.

But, ultimately, we swallowed our pride and accepted the origami. It was a series of torn strips folded into a rectangular cylinder. A simplified diagram of the cottage as viewed from the south – that's what it looked like. When we tilted the right side of the rectangle, the left side tilted at the same angle. The rectangle became a parallelogram. “Oh, I get it!” Yozuki was as happy as an elementary school student. ...This girl was in college. However, it was true that the origami made it easier to understand.

So, I tilted the right side again, this time holding the left side in place with my finger. As a result, the top of the rectangle became crooked. Well, of course. It was physically impossible to only tilt one side of the rectangle. If you tried to force it, something else would definitely bend alongside it.

That's when it hit me.

“Maybe this cottage is also like this.”

“Yes, that's how it is,” Mitsumura said with a nod. “When the east wall tilts, there must also be something else that tilts. Or rather, it must have been built to tilt. And the only places that can tilt with it are the opposite wall and the ceiling. We've determined that the east wall can't tilt, so we can only conclude that it's the ceiling.”

That was the only sensible conclusion. The new question was...

“I wonder which way the ceiling tilts,” I said.

There were two ways it could have gone. There were two types of folds: so-called “valley folds”, where the ceiling sank into the room, and “mountain folds”, where it raised away from the room.

And if it was a mountain fold, then something very interesting happened. Since the ceiling was rising away from the room, it would create gaps between the ceiling and the north and south walls, and the more the east wall tilted, the larger the gaps would grow, until eventually, they'd be large enough for a person to pass through. In other words, if the ceiling formed a mountain fold, there was a secret passage to escape from the locked room. If the culprit used it to escape, than the locked room would be solved. However, if the ceiling made a valley fold, than the ceiling would sink into the room, and there would be no gaps between the north and south walls. Therefore, there would be no secret passages, and there would still be no way for the culprit to escape the locked room.

Therefore, whether the ceiling made a mountain or valley fold was of critical importance. “Which way does the ceiling bend?”

Mitsumura shot me down.

“It's a valley fold.”

So the ceiling folded into the room? That meant there was no way to escape through the space between the wall and ceiling.

I tried to fight back.

“And what is your basis for saying that?”

“I mean, you were there with me when I climbed up on the roof, right?” Mitsumura said. “I placed that ping pong ball on the ceiling and it rolled towards the center. That means the roof was already tilted slightly into the room to begin with. It's hard to imagine the roof folding into a mountain fold from that position, unfortunately. Even when the ceiling tilts, no hidden passages are formed. But that's fine. I can still explain every detail about the scene.”

My lips loosened into a grin at her confidence.

“You really like stalling, don't you?”

Mitsumura grinned back at me.

“Since I'm playing the role of detective, part of my job is building the audience's anticipation, much as it pains me. Well, let's begin the demonstration, then. It looks like she's just arrived.”

Mitsumura said that, looking out towards the road. There was a large truck coming towards us. No, not a truck. It was a strange vehicle. It looked like it had a huge metal long strapped to the top. It was...

“The Battering Ram?”

It was the weird vehicle I'd seen in the garage. Eventually, the car veered off the road and came to a stop near the cottage. The person driving was Ms. Chiyori.

“Why did I agree to this?”

Ms. Chiyori opened the driver's side window and complained. Mitsumura rather roughly expressed her gratitude, yelling “Thank you, Ms. Kurokawa!” She looked like an evil magistrate.

“Now, proceed as planned.”

“But of course.”

Ms. Chiyori laughed like an evil magistrate's sniveling henchman and drove off. She stopped facing the east wall of the cottage, about 100 meters away.

“What are you going to do?” Yozuki asked, sparkles in her eyes.

“Of course, we're going to reenact the locked room trick,” Mitsumura said. “Well, please watch closely. I'm sure it will be... enlightening.”

Mitsumura let loose an evil laugh, then coughed a few times and resumed speaking.

“Last night, when Mr. Poirotzaka was killed, he was lying in his bed sleeping, just like the French doll,” Mitsumura said, pointing to the cottage's south wall. There was a large window there, allowing a clear view of the interior. “And Mr. Poirotzaka locked his door before going to sleep, so he was already in 'a locked room'. Therefore, if he were to die in this state, the crime scene would bee a locked room.”

That was true, but it was also completely impossible. Of course, it wasn't difficult to kill Poirotzaka like this, and there were any number of existing tricks able to kill someone without entering the locked room. The problem was how Poirotzaka was killed. His head had been cut off in a locked room. I couldn't believe such a devilish feat was possible for a mortal culprit.

And I told her as much.

“That's completely impossible.”

“It is possible, if you use The Battering Ram.”

Mitsumura turned her attention to the special vehicle that Ms. Chiyori was in.

“As I've said several times now, the key to this incident is that the east wall can tilt. When I noticed that, I wondered, how far can it tilt? Unfortunately, there was no way to check, since tilting the wall required great force, more than any amount of humans could provide.”

Mitsumura stroked her black hair.

“So, I thought we just needed something stronger. At first, I was thinking of ramming it with a truck, but I found a vehicle that was better suited to the purpose. A vehicle constructed for the sole purpose of hitting walls.”

Of course, that vehicle was...

“The Battering Ram...”

The moment Yozuki mumbled that, Mitsumura raised her right hand. I saw Ms. Chiyori nod from the driver's seat. Then, The Battering Ram 100 meters away took off.

It was slow at first, but it gained speed gradually.

The Battering Ram was accelerating. Its massive body, weighing dozens of tons, gathered more kinetic energy. By the time it reached the cottage's wall, it had become an enormous cannonball.

The sound was like Thor using Mjolnir to strike a steel temple bell.

The Battering Ram's battering ram slammed into the east wall of the cottage. At that moment, the east wall bent inward at unbelievable speed, and the ceiling folded into a valley fold at the same rate.

And we saw it.

The valley fold fell into the room at high speed, and its tip soon formed into a sharp edge.

In other words, the bend in the ceiling had formed into a gigantic blade that was rapidly approaching the floor.

The entire cottage was a gigantic guillotine.

The guillotine's blade sliced the head clean off the sleeping French doll.

Yozuki and I were stunned speechless.

“This is...”

“As you can see, Kuzushiro,” said Mitsumura, calm as ever, “This cottage was designed to be used with The Battering Ram. When The Battering Ram hits it, the person inside is decapitated. It was designed by Richard Moore, the island's former owner, as the ultimate in playfulness. It's a cottage designed solely for decapitating people in locked rooms.”

I was dumbfounded.

“I think it's debatable just how playful that decision is...”

No one could say what Richard Moore's intentions were anymore. However, it was certain that this trick had been used in this murder, and indeed in the “Decapitation Chamber of Wire Mesh Island” cases that had happened twice in the past.

According to what Ms. Hitsujiko had told us earlier, the cottage was made of an extremely strong alloy. Probably because of that, the wall that had just been hit by The Battering Ram didn't have a scratch. That fact was the strongest evidence that the cottage was intentionally designed to be used with The Battering Ram.

The cottage had a lattice pattern engraved on both the outside and inside of the building. I realized that was to hide the fold where the ceiling bent inward. The same design covered the entire building because it would stand out too much if only the ceiling had the lattice pattern.

In any case, the culprit, the Living Locked Room Library, had used this cottage's trick to commit murder. Without even stepping into the room, they killed Poirotzaka inside. Then, the toy rabbit found under the bed wasn't left there when Poirotzaka was killed, but placed underneath it before Poirotzaka was killed.

“Huh?” Yozuki exclaimed.

“Wait, what about the huge sword stolen from the entrance hall?”

“Ah, that was the culprit's attempt to mislead us,” Mitsumura said. “By pretending the sword was the murder weapon, they tried to distract us from the trick of the cottage, although they didn't succeed. Because the bed was destroyed. Only someone living in a fantasy world could ever believe that a sword could clean cut a bed in half.”

Actually, the ceiling itself had come down with enough force to snap the bed in two. Then I remembered. Come to think of it, the bed was fixed to the floor of the cottage. Had that been done to ensure the victim was in an optimal position to be decapitated with pinpoint accuracy?

Everything had been carefully prepared. I noticed something else, too.

“So, there was a reason the culprit had to remove the great sword from the entrance hall of the mansion.”

“Yes, there was. That sword wasn't actually used in the crime,” Mitsumura said. “If the police were to investigate it later, they would find out it wasn't the real murder weapon because the blade would show no traces of blood, right? That's why they had to hide the sword. This island is quite large, so if they took it out and buried it in the forest somewhere, it would probably never be found.”

I nodded. Did that answer all my questions? No, wait...

“There were two murders in this cottage in the past,” I said. “The Decapitation Chamber of Wire Mesh Island is one of Japan's Four Great Locked Rooms. Why couldn't the police find this mechanism during their investigation of that case?”

It was true that the east wall didn't move unless you applied a lot of force, so it would be hard for the police to realize the truth. But in this Golden Age of Locked Rooms, using X-rays and things like that to examine crime scenes was standard procedure. In that case, wouldn't the mechanism allowing the ceiling to bend have been discovered?

Mitsumura said “Some metals are resistant to X-ray penetration.”

“Like lead, for example. So if the alloy used in the cottage's construction is a metal that can't be X-rayed, it would be difficult to find the mechanism in the ceiling. Or rather, Richard Moore must have designed the cottage with that in mind. If he filled the ceiling with dummy grooves and cuts, the real seam would be hidden in the forest of lines. In the end, even after searching the entire room, they concluded that there weren't any tricks.”

I was satisfied with that explanation. He was a mystery loving freak who built a cottage like this in the first place, so there was nothing unusual about him going that far.

“And one more thing. The fact that the culprit used this trick to kill Mr. Poirotzaka is itself significant,” Mitsumura said. “That means the culprit knew about this trick. I don't know if they investigated or discovered it by chance, but it would be impossible for someone who only arrived on the island the other day to commit this crime. The culprit must be a resident of Wire Mesh Island.”

After she said that, a small smile formed on her lips.

“If you think about it normally.”

I smiled bitterly at her words. Certainly, if you think about it normally. But there was an exception to every rule. So we still weren't any closer to finding the culprit's identity.

At any rate, two of the locked rooms, the locked basement and the Decapitation Chamber, had been solved. There were now only two left, the locked Tower of the Cross where Gentleman was killed, and the Ms. Breakfast's cottage.

“It's two in the afternoon,” Mitsumura said, looking at her watch. “If possible, I'd like to resolve this case before sundown.”

“Well, yeah,” I said. That would be ideal.

“I suppose there's no other way. Desperate times call for desperate measures,” Mitsumura told me, stroking her black hair. “Let's split up. You and I will take one locked room each.”

My eyes went wide at the unexpected request.

“Wait, I'm going to solve a locked room?” 

“Yes, that's what I said.”

“But why me?”

“If I have to work like a dog, than so do you.”

“I'm not a dog though.”

“I know. Dogs are much cuter.”

I mean, that one was just true.

She must have noticed the look on my face. Mitsumura looked at me, then tilted her head to the side.

“Oh? Kuzushiro, could it be that you aren't confident in your abilities?”

“Not at all.”

“That's pathetic,” Mitsumura said in surprise. Then she looked at Ms. Chiyori, who had come out of The Battering Rom, and said “It can't be helped. As a special bonus, I'll let you take Ms. Kurokawa with you.”

“Please don't treat people like buy one get one free deals.”

“And in exchange, I'll take Yozuki.”

Mitsumura completely ignored Ms. Chiyori's protests and hugged Yozuki's arm. Yozuki was surprised.

“Wait, I'm teaming with Mitsumura?”

“Yes, that's how it is,” Mitsumura said with a demure nod. “So, Yozuki, will you be my Watson?”

“Your Watson...”

Yozuki looked deeply moved by the offer. She was a simple girl at heart. Yozuki pumped her fists.

“Yes! I will be your Watson!”

Thus, the greatest detective duo since the inhabitants of 221B Baker Street was born. And for some reason, the sight made me a bit uncomfortable. Mitsumura quickly noticed and grinned at me.

“Oh, Kuzushiro, are you jealous?”

“Don't be ridiculous,” I immediately shot back. She was completely off the mark. Why should I have been jealous? So I protested. “I don't remember being your Watson in the first place. The only reason I let you treat me like that is because we've been stuck together since middle school and I've long since learned there's no point in arguing.”

I made Mitsumura angry. She said in a clearly displeased voice, “Oh, I see. Then we'll go with these pairings.” She hugged Yozuki's arm again. “I hope you don't regret this later.” This was her idea, why was she so upset? I didn't get her.

“Well, anyway,” Mitsumura said, obviously trying to change the subject, “Let's divide up the rooms now. Kuzushiro, your team can decide what you want.”

In other words, whether we wanted to be in charge of the locked Tower of the Cross or Ms. Breakfast's locked cottage.

“Hmm,” I hmm-ed, then asked my partner for her opinion. “What should we do, Ms. Chiyori?” Ms. Chiyori responded with confidence.

“Whichever one is easier.”

She had no confidence. What happened to all her aggression earlier?

But I completely agreed with her. The question was, which one was easier?

“We won't know until we've already solved it. That's what a locked room is.”

“Kasumi, what are you talking about?”

Yozuki sounded worried about me. In the end, I decided to go with the locked room with the simpler set-up. In other words...

“Ms. Breakfast's cottage.”
“Alright then, we'll take the Tower of the Cross.”

Thus, the room allocation was complete. We split into teams and began our respective investigations.

“Let's go, Yozuki.”

“Yes, Ms. Holmes!”

Yozuki was excited. She was a straightforward girl, so she must have been happy to have been cast as the Watson.

As I watched Yozuki and Mitsumura's backs walk away, I felt a little sad.

Yozuki Asahina, having teamed with Shitsuri Mitsumura, went first to the Tower of the Cross, the scene of the incident. When she pressed the button on the outer wall, the room on the right side of the cross descended like an elevator. One it was on the ground, Yozuki and Mitsumura opened the door and entered the right bar of the Tower of the Cross.

“Hmm, so this is the inside of the Tower of the Cross.” Come to think of it, she had been “imprisoned” when the body was discovered. After Mitsumura took an interested look around the room, her eyes fixed on the door.

“Is this door the type that doesn't have a thumb turn?”

Yozuki nodded.

“That means you can't use any trick like turning the thumb turn from the outside.”

“Yes, Yozuki, you're right,” Mitsumura said, smiling at her. “You understand quite well.”

“Ehehehe, praise me more.”

Seeing Mitsumura's attitude, Yozuki thought that she was the sort of person who did care about others. She was a girl who respected her elders. On the other hand, she was extremely cold to her peer, Kuzushiro.

“Something else I've noticed,” Mitsumura said as she wandered the room. “There are no windows in this room, and the only place the culprit could hide was the toilet. Therefore, the criminal entering and exiting via the window and them hiding inside the room are both impossible. Therefore...”

Mitsumura opened the door and exited the Tower of the Cross. Then, leaving the door open, she walked back and forth in and out of the room several types. How mysterious. Yozuki couldn't take it anymore and asked.

“Mitsumura, what are you doing?”

“I'm checking the thickness of the walls and ceiling,” Mitsumura said. “The walls are each about 30 cm thick. The floor and ceiling are the same. If the walls or ceiling are too thick, there's a chance there's something hidden there.”

I see, Yozuki thought.

“Something like a secret passage.”

“Exactly right,” Mitsumura said, tapping steadily on the walls on floor for a while. Then she said “We should check the ceiling as well,” and bent down on the spot. When Yozuki looked at her in confusion, Mitsumura looked up at her and said “Get up on my shoulders.”

So she wanted Yozuki to be the one to examine the ceiling.

“Well, if you insist.”

Yozuki sat on Mitsumura's shoulders, straddling her neck. It was kind of fun. Mitsumura grabbed Yozuki's legs and stood up with a grunt. She was surprisingly strong. Yozuki, on Mitsumura's shoulders, was brought up to the ceiling, which she started tapping. She spent several minutes searching the ceiling, but didn't find any hidden doors.

“Hup!” Yozuki hopped off Mitsumura's shoulders.

“Well, I expected as much,” Mitsumura said. “The only possibility is that the culprit entered and exited via the door. To be precise, it wasn't just the culprit, but also Dr. Iori, who had been imprisoned here, and Mr. Gentleman, whose body was found in this room.”

Hearing it said again, it felt like a truly impossible crime. There were two mysteries to the incident: ① Dr. Iori, who was supposed to be inside the locked room, was taken outside, and ② Gentleman's corpse was found in the locked room in her place.

“Both those mysteries can be solved at once if the culprit can unlock the door,” Mitsumura said. “So now let's investigate Mr. Shitsugi's cottage, where the key to the tower was kept.”

The key to the Tower of the Cross was being kept in a small room in Shitsugi's cottage. Mitsumura entered that small room and picked up the key to the Tower of the Cross from the hook on the wall.

“In short, if you can get this key out of this room, you can unlock the door to the Tower of the Cross.”

Yozuki had realized that already. But the problem was significantly more complicated.

“The key ring is too big to fit through the gaps in the iron bars on the door.”

Yozuki looked at the ring chained to the key in Mitsumura's hand.

The key to the Tower of the Cross had a 10 cm long chain, and on the other end of the chain was a ring with a diameter of 20 cm. The key, chain, and ring were all completely integrated and couldn't be disassembled. Therefore, as long as the key ring couldn't pass through the iron bars on the door, the key couldn't be taken out of the room.

“Hmm...”

Mitsumura tried to fit the door through the iron bars. The door had a peephole at about eye level, a rectangular gap about 10 cm tall and 40 cm wide. Since it was divided into four equal parts by the vertical iron bars, each gap in the bars formed a 10 cm x 10 cm square. The diagonals of the squares were approximately 14 cm each. That meant in order to pass the ring through any gap in the bars, it would have needed a diameter less than 14 cm.

However, the ring had a diameter of 20 cm. Therefore, the key ring couldn't pass through the iron bars. And that meant the key couldn't pass through them, either.

“Hnngh!”

Mitsumura tried to pass the key through the gap, but no matter how hard she struggled, it didn't fit. Eventually, she gave up and turned back to Yozuki.

“As you said, it's impossible to fit the ring through the gap in the bars.”

“Yeah, you're right,” Yozuki nodded. “Then, maybe they transformed the ring itself?”

“You mean they changed its shape to one that could fit through?” Mitsumura looked down at the ring in her hand. Then she slowly shook her head. “No, that's impossible. The ring is extremely solid, and it's shaped in a perfect circle. If the culprit had forced it into another shape, there would be no way to return it to this flawless shape.”

It seemed they had to give up on taking the key to the Tower of the Cross out through the iron bars.

So the next thing was...

“This.”

Yozuki left the small room and retrieved the key safe from the drawer in the cottage's wall. That was where the key to the small room had been kept until Gentleman's corpse had been found that morning. The key safe had five keyholes which took five separate keys held by five separate people. Therefore, unless all five of them were accomplices, there was no way to get the key to the room out of the safe...

Yozuki started.

“Unless there were two safes.”

The culprit broke the original safe and used the key to the small room. Then, when they were done, they put it back in a different, but similar looking safe with five keyholes. By doing that, when the incident was discovered and the key was taken from the safe, the safe would be found locked.”

“I'm a genius...”

Yozuki was amazed by her own intellect. Had she discovered her true power? It seemed becoming Mitsumura's Watson had caused her hidden talent to bloom. No, wait. If things continued like that, wouldn't Mitsumura and Yozuki's positions be reversed? Yozuki would be Holmes and Mitsumura would be Watson. Well, Yozuki didn't think that sounded so bad.

“What are you smiling about?”

Mitsumura looked at Yozuki dubiously. Yozuki coughed a bit. That was close, she'd almost gotten carried away. As a detective, one must always remain cool and collected.

“Anyway,” Yozuki said, “the mystery has now been solved.”

Mitsumura looked at her with “What the hell are you talking about?” written all over her face.

“That doesn't solve anything.”

“Eh? No way.”

“Think about it for a second,” Mitsumura said. “According to your theory, the key safe was replaced with a different one, right?”

“Yeah.”

“Then no matter how similar they looked, they would be different. And that means they would need different keys to open. If, when the incident was discovered, you tried to open a fake safe with the real keys – one of which you held, I might add – they wouldn't have unlocked the safe. But your keys did unlock the safe. That means it was the real safe and not replaced with a fake.”

It was a complete, logical rejection. Yozuki said “But, but...” as she desperately searched for a rebuttal.

“But what if, say, the keys to the real safe that we all had were replaced with the keys to the fake safe?”

“So the culprit snuck into everyone's cottages in the middle of the night and swapped your keys?” 

“Yeah, that's right. Then the plan to replace the safe could be used, right?”

“Well, I suppose it could,” Mitsumura said, putting her hand on her chin. “But if that were an option, then why didn't they just steal the keys without leaving the fakes behind? That would allow them to open the original safe.” 

“Oh... yeah.”

She hadn't thought of that.

“Besides, that doesn't seem possible. Sneaking into a locked cottage or room in the mansion and stealing the key without anyone noticing a thing... The culprit isn't a ninja.”

Not a ninja... right. And apparently, as long as the culprit wasn't a ninja, Yozuki's theory wouldn't work.

“Alright, then.”

Yozuki thought of something new. What about this? When the incident was discovered, Hitsujiko was the one to unlock the safe. So, what if she'd swapped the keys at that time? In other words, she had used the fake keys with the fake safe from the beginning, and secretly hidden the real keys. Yozuki felt like she was onto something. But when she took the keys to the safe, did Hitsujiko really have time to make the swap? After all, everyone was paying attention to her at the time... So, how did the culprit get into the locked room...? 

“Uuuuuhg...” Yozuki held her head.

“What's the matter?”

“My head's starting to hurt.”

“Well, you don't use it much.”

What the heck!? That was so mean!

Mitsumura realized that she'd let that slip and rapidly turned pale.

“I-I'm sorry, I didn't mean it like that!”

How else could she have meant it?

Yozuki took a deep breath. And then she angrily began examining the safe. She wanted to find a way to get that key out of the box. She couldn't let it end like that. She would have her revenge on Mitsumura!

Then, Yozuki saw her wish come true. When she turned the safe over and looked at the back, she made an expression of surprise. Mitsumura tilted her head.

“Yozuki, what's wrong.”

“Look here,” Yozuki said, pointing to the back of the key safe. “I think there's a gap here.”

Yozuki looked at the back of the safe again. It was so thin it was hard to see, but there was a slight gap in the back of the safe. It was a thin rectangle, like the back of a camera.

Was there something there?

After staring at the back of the safe for a while, Mitsumura pulled a Swiss army knife from her pocket. Seeing that, Yozuki tilted her head.

“What are you going to do with that?”

“Of course, this.” Mitsumura pulled the blade from the Swiss army knife and inserted it into the back of the safe. Then, she levered it until the back cover popped open.

“This is...!”

Yozuki and Mitsumura's voices overlapped.

When they removed the back cover, they made a surprising discovery. There was another keyhole there.

In the safe with five keyholes, they'd found a sixth keyhole.

“What is it?” Yozuki asked timidly.

Mitsumura sounded equally confused. “Could it be, this keyhole can open the safe? In other words, it might be possible to open this safe with only the sixth key, without using the five keys you all split amongst yourselves.”

So... Yozuki had found something important?

“Yes, it's something very important. You've made an amazing discovery, Yozuki.”

“Ehehehe, I guess I have.”

She felt really good.

“This is important,” Mitsumura said, placing her hand on her chin. “I wonder where the key that fits this sixth keyhole is. Perhaps Ms. Hitsujiko knows. Let's go ask her.”

After parting ways with Mitsumura and Yozuki, Ms. Chiyori and I headed to Ms. Breakfast's cottage, the crime scene. We started by double checking the facts of the case.

The door had a thumb turn on the inside, which was, of course, set to lock at the time the body was discovered. All the windows in the room were fixed. Therefore, the possibility that the culprit could have entered or exited through any of them was zero.

“It's a perfect locked room.”

Ms. Chiyori sounded disgusted by the prospect. I'd also checked the hinges of the door, but they all looked quite old, so I didn't think this could have been the same trick as the basement's locked room.

“Hmm...” Ms. Chiyori went as she searched the room. She looked like she was being forced to investigate against her will. She seemed tired of all the locked room murders that had been coming one after another since this morning. “By the way,” I said.

“Yes? What is it?” Ms. Chiyori replied, looking back at me from where she'd been checking under the bed.

“I've actually wanted to ask this for a while now,” I told her. “Be honest. What exactly is your relationship with Mitsumura?”

I felt like the relationship between them was too strained to just be defendant and judge. That's why I thought there may have been some connection between them beyond the trial.

Ms. Chiyori looked extremely displeased to be asked, then gave me a contemplative smile. “Oh, is that all?”

“To be honest, nothing really happened between us. We only ever met in court; we never even spoke outside of it. We have no relationship beyond judge and defendant. But...”

“But?”

“I was convinced the moment I saw her. That's a rare feeling.”

I was intrigued.

“What were you convinced of?”

“That she was a murderer... That's what I felt.”

I couldn't keep the smile off my lips.

“What a coincidence. I agree completely.”

The first locked room murder case in Japan took place three years ago, and I was convinced the culprit was Shitsuri Mitsumura. It was just my intuition, and I had absolutely no basis for that belief, but in my mind I was as sure as the sun would rise tomorrow.

Apparently, Ms. Chiyori thought the same.

“That's why I had to endure this feeling of disgust all through the trial,” Ms. Chiyori said. “Even though she'd definitely killed someone, she was so shameless about it. It made me sick. Of course, as a judge, I couldn't let those feelings show, but I think she sensed them anyway. That's why she hates me so much.”

It must have been tough, being viewed like that by a judge who was supposed to be impartial. Mitsumura had told me previously that during the trial, Ms. Chiyori and looked at her like trash. I thought she was being paranoid, but it turned out she wasn't wrong.

So...

“If you were so sure Mitsumura was the culprit, why did you give her a not guilty verdict?”

That was what I didn't get. After Ms. Chiyori showed me a bitter expression, she said “Because the law is strict.”

“Judges are generally pretty serious people, but I'm especially serious. It might not seem like it sometimes, but I'm so serious that I hate myself. That's why I could never give a verdict I didn't agree with. That's why I had no choice but to give the not guilty verdict. I just couldn't accept the theory the prosecution presented at the trial.”

The theory presented by the prosecution...

“Do you mean the locked room paradox?”

Ms. Chiyori nodded at me.

The Locked Room Paradox was a theory created by the prosecutors of the first Japanese locked room murder three years ago. The theory involved two conditions:

① The scene is a locked room.

② The crime must have been a murder.

If condition ① was met, than there was no one in the world who could enter the crime scene. To put in bluntly, that meant it wasn't a murder. However, that clearly contradicted condition ②, which stated that it was a murder. In other words, a locked room murder satisfied conditions ① and ② at the same time, creating a contradictory state of simultaneously being “murder” and “not murder”. In a way, it was similar to the Schrodinger's cat paradox. That was the locked room paradox presented by the prosecution.

And the only way to escape the paradox was to reject either condition ① or condition ②.

Therefore, the prosecutor's office decided to ignore condition ①, “The crime scene is a locked room”. Since condition ② stated that “the crime scene must have been murder”, condition ①'s “no one could commit the murder” could be reversed to say “everyone had an equal chance to commit the murder” and, by extent, “it doesn't matter who the culprit is”. Since no one could do it, it doesn't matter who did it – it was blunt, and in its own way, extremely rational. Since there was a murder, someone was the murderer. If it was equally impossible for anyone to be the murderer, then it wasn't really different from it being equally possible for anyone to be the murderer. Either way, everyone was equal – that point hadn't changed.

That was the major difference between locked room tricks and alibi tricks. In the case of an alibi trick, the crime only became impossible for the person who performed the trick, and the crime could still be pinned on someone else with no alibi. But locked room tricks didn't work like that. If a trick was used to make the scene a locked room, it automatically became impossible for anyone to become the culprit, and there would be no resolution to the crime.

“But isn't that strange?” said Ms. Chiyori. “If it's impossible for anyone to commit the crime, than everyone in the world should be acquitted.”

What she said was also correct. And the idea was similar to what I'd heard from Mitsumura, the defendant of the case three years ago. Although the two appeared to be opposites, they were very similar. Maybe that was why they were so incompatible.

I spoke to her.

“You're very serious, Ms. Chiyori.”

Ms. Chiyori looked frustrated.

“I'm tired of hearing that,” she said brusquely. “That seriousness has ruined my life. In case you've forgotten, I was raked over the coals.”

Certainly, it was terrible. “Chiyori Kurokawa is scum”, “Chiyori Kurokawa's incompetence”. Words like that went flying on the internet. Without doubt, she was the most controversial judge in Japanese history. Though considering the sentence she'd handed down, that might not have been avoidable.

“Alright, enough of this. Let's get back to the investigation.”

Ms. Chiyori said that and went back to looking under the bed. I was about to join her when I suddenly realized I was extremely thirsty. 

“I'll go get some water.”

I said that and left the cottage. There was a refrigerator inside, so I could have borrowed a drink from there, but I didn't feel comfortable drinking something kept at a murder scene.

So I went back to my cottage and took out a plastic water bottle from the fridge. I downed about half of it in one breath. Then I suddenly remembered I had business with Yozuki. So I decided to go find her before returning to Ms. Chiyori.

In order to obtain the the key to the keyhole on the back of the safe, Yozuki headed back to the mansion with Mitsumura, who held the safe in her hands. Hitsujiko might have known where the key was. With that thought in mind, they searched the mansion for her. However, Yozuki looked in completely random places, and Mitsumura chided her, saying “Yozuki, your investigation is too unfocused.”

After opening a random series of doors, Yozuki arrived at the library on the mansion's first floor. The library's atmosphere was tranquil, lined with antique bookshelves about the same height as those in an average high school. It was quite impressive for a private collection. As expected from the mansion of the great mystery writer Richard Moore.

As she walked through the library, she saw Otomigawara. She was standing in front of a bookshelf, looking down at a book, but when she noticed Yozuki and Mitsumura, she looked up.

“Ah, Ms. Yozuki, Ms. Mitsumura. Can I help you?”

“We're looking for Ms. Hitsujiko,” Mitsumura said.

Otomigawara daintily tilted her head to the side.

“Hitsujiko? Now where has she gone?”

That was her answer. Apparently she didn't know either.

Well, they should have gone somewhere else, then, but it was such a wonderful library. She was curious what kinds of books were in the collection. Yozuki wasn't that big a reader, but she did finish about a book a month. So she was intrigued, and looked at the books on the shelves. Books with titles like “The XXX Murders” and “The XXX Murder Case” stood in lines.

“Did you collect all these books yourself, Ms. Otomigawara?” Yozuki asked.

“No, most of the books in this collection were left behind by Richard Moore,” Otomigawara replied. “When I acquired this mansion, I was told by the real estate agent. Apparently, the previous owner didn't sell them.”

“So, this book was also part of Richard Moore's collection?”

Yozuki pointed to the book in Otomigawara's hand. Otomigawara handed it to Yozuki, saying “No, this is one I bought myself.”

She looked at the book she'd been given. The title was “And Then No One Was Left”.

“And Then No One Was Left...”

Yozuki couldn't help reading the title out loud. Even she, who didn't know much about mysteries, could recognize that it was a play on Agatha Christie's And Then There Were None.

This was her first time seeing a book that was a parody (or was it a homage?) like this. She couldn't resist the urge to look inside. Then her eyes went wide. There was a cast of characters page at the beginning:

Dramatis Personae:

Lawrence Wargrave..... Former Judge

Vera Claythorne..... P.E. Teacher

Philip Lombard..... Former Army Captain

Emily Brent..... Old Lady

John MacArthur..... Retired General

Edward Armstrong..... Doctor

Anthony Marston..... Young Man

William Blore..... Former Police Inspector

Thomas Rogers..... Butler

Ethel Rogers..... Butler's Wife

“Whoa, all the characters are foreigners.”

Yozuki exclaimed in surprise. Mitsumura peered at the page over her shoulder and appeared to notice something.

“These are the same characters as in And Then There Were None.”

“Oh, that's right!” Yozuki said, even though she'd never read it before. “That's correct,” said Otomigawara.

“This novel is a pastiche of And Then There Were None, using the same cast and setting. In the story, the same characters as in And Then There Were None are killed one after the other, but there's a major twist at the end.”

Huh, it sounded kind of interesting. Just as she was thinking that, the door to the library suddenly opened. The person who came through was Kuzushiro.

“Kasumi? Is something wrong?”

When Yozuki asked that, Kuzushiro replied “No,” and closed the door behind him. “I just realized I forgot to give get something important from you.”

Hearing that, Yozuki and Mitsumura looked at each other. Something important? Like her heart? No that probably wasn't it. So what was it?

“What is it?” Yozuki asked, tilting her head. Kuzushiro scratched his head and held out his hand.

“It's the key cards to the cottage.”

Yozuki and Mitsumura exchanged another look. Then, Yozuki remembered she was the one keeping them and rummaged through her pocket. Fortunately, she found both card keys quickly and handed them over to Kuzushiro. The key cards to Ms. Breakfast's cottage. The scene of the crime had been locked with a card key, so it was true that without those, it would be difficult to solve the mystery.

As Kuzushiro put the cards in his pocket, Mitsumura asked him something.

“So, how has your progress been?”

Kuzushiro furrowed his brows.

“We're clueless.”

“Well, that's a shame,” Mitsumura said with a grin. “Though not unexpected.”

“Is that a fact?”

Kuzushiro left the library. After Mitsumura showed Kuzushiro off, she turned to Yozuki.

“We should go, too. We have to find Ms. Hitsujiko.”

Fortunately, they were able to find Hitsujiko soon after leaving the library. When they showed her the safe and told her about the keyhole on the back, she smiled at them.

“So you found it.”

Yes, they had.

“Why is this trick here?” asked Mitsumura.

“That's what Richard Moore did,” Hitsujiko said. That famous mystery writer's name had come up again.

“This safe was custom made by Moore,” Hitsujiko said, pointing to the safe still in Yozuki's hands. “It was inherited by the subsequent owner of Wire Mesh Island. I am told Moore used to call it 'Bel's Box'.”

“Bell's Box?” Yozuki said. “Like the guy who made the telephone?”

“That's not it, Yozuki,” Mitsumura said. “It's Bel, from the story of Bel and the Dragon in the Old Testament.”

“As expected, you are quite knowledgeable,” Hitsujiko said with a nod. “I don't know much about it, but as I understand, in discussions of the origin of the locked room mystery, one name often mentioned alongside Poe's 'Murders in the Rue Morgue' is the Old Testament's 'Bel and the Dragon'. In short, it's a story in which a secret passage is used to collect offerings of food from a sealed temple.”

“It sounds like a Japanese folktale,” Yozuki said.

“Indeed, though I haven't read it, I thought the same thing,” Hitsujiko laughed. “The solution to the mystery is that the priests were sneaking into the temple through a secret passage and eating the offerings themselves. It is much like a Japanese folktale. In short, Bel and the Dragon is a story about a secret passage, and the removable back of this safe is a secret passage like the one in Bel and the Dragon. In other words, it's a secret trick allowing the key inside to be taken out of the safe.”

Yozuki understood, but she also didn't. But even more than that, what she really didn't understand was...

“Why did Richard Moore deliberately build a safe with a secret trick?”

When Yozuki asked that, Hitsujiko nodded sympathetically. “I thought the same thing,” she said.

“So I asked Lady Otomigawara, and she replied 'Of course, it's because Mr. Moore loved mysteries.”

At that, Mitsumura nodded sagely.

“That makes sense.”

It really, really didn't. But if Mitsumura was satisfied with that answer, she guessed it was fine. This was a discussion that Yozuki, who had no interest in locked rooms, had no voice in.

So she decided to move on.

“So where is the key to this safe?”

Hitsujiko said “That is...”

She seemed somewhat disturbed. Mitsumura and Yozuki exchanged a look.

Hitsujiko guided Mitsumura and Yozuki to a room in the mansion. After opening the door and stepping inside, Hitsujiko took the key out of the desk drawer.

“This is the sixth key to the safe.”

When Yozuki retrieved the key, she inserted it into the keyhole in the back of the safe. She turned it, and the lock clicked open. The back of the safe opened.

Mitsumura and Yozuki both gasped. So as long as you had the sixth key, you could freely take the key to the tower from the cottage.

But...

“That's actually not the case.”

Hitsujiko said that and led Yozuki and Mitsumura back out into the hall. There, she pointed at the ceiling. There was a small surveillance camera installed there, pointing directly at the door to the room where the sixth key had been.

“So,” Mitsumura said with a thoughtful expression, “You're saying that if someone took the key from this room, they'd have been seen on the surveillance camera?”

“Yes, that's correct,” said Hitsujiko. “The windows in that room don't open, so the only way in or out is through the door on the camera feed.”

Yozuki wanted to cry.

“By the way, what did appear on the camera feed?” asked Mitsumura.

“Naturally, I've checked it already. No one appeared on it, not even myself and Lady Otomigawara,” Hitsujiko said. “Both Lady Otomigawara and I knew about the secret panel on the back of the safe. That's why after the incident, Lady Otomigawara asked me to check the camera footage. If someone had appeared in the footage, the scene would no longer be a locked room.”

Mitsumura thought for a moment. “I see. Just to be certain, may I see that footage?” Hitsujiko replied “Yes, that's fine,” and led Mitsumura and Yozuki to the security room where they could check the camera's records.

They went over the footage again. To skip to the end, nobody had gone into or come out of that room in the past two weeks. Not a single person appeared on the security footage from the time Hitsujiko entered the room with a set of cleaning supplies two weeks ago to when Yozuki and Mitsumura arrived looking for the sixth key.

Which meant no one could have taken the sixth key. Yozuki groaned and lifelessly asked,

“There isn't a spare sixth key, is there?”

“No.”

“Then we're cooked.”

Yozuki held her head in her hands. She mentally reviewed the mystery of the locked Tower of the Cross.

First, the corpse of Gentleman was found inside the Tower of the Cross. The door to the tower was locked, and the key was kept in a small room in Shitsugi's cottage. That room was also locked, and the key was kept in a portable safe. And now the key to the safe was kept in a room in the mansion observed by a security camera, which was also a sort of locked room. So to simplify, there was a locked room, and the key was in a different locked room, whose key was in a locked safe, whose key was in another locked room. This whole case was...

“A matryoshka.”

“Huh? What did you say?” Mitsumura asked, surprised.

“Nothing, I'm just talking to myself.”

“Hmm... Well, that's fine.”

Mitsumura went back to thinking. Seeing her like that, Yozuki spoke her heart.

“Let's just give up, Mitsumura,” she said, patting her shoulder. “There's no way to get the sixth key out of a room under surveillance.”

Mitsumura obediently nodded and said “That's true.”

“Indeed, a method to do so doesn't exist. At least, if you think about it normally.”

She'd said something suggestive.

Then, Mitsumura stroked her hair, then took a hair tie from her pocket and set her black hair in a ponytail. Mitsumura with a ponytail was a rare and valuable sight.

“Mitsumura? What are you doing?”

When Yozuki asked her that, Mitsumura looked at her with a gentle smile.

“I can concentrate better with my hair in a ponytail.”

“That's the first I'm hearing of this!”

Yozuki had no idea she was hiding a secret move!

Mitsumura closed her eyes. And when she'd opened them, they no longer held any warmth.

Yozuki felt a chill. Her eyes were frighteningly cold. She looked like a murderer. Of course, there was no way a nice young girl like Mitsumura had ever killed anyone before.

“Yozuki,” Mitsumura said with her cold eyes. “Please give me a minute to organize my thoughts.”

Mitsumura said that, then silently put her hand on her chin. Yozuki went silent so as not to disturb her. However, despite her cooperation, Mitsumura immediately turned to her with a warm smile.

The light had returned to her eyes.

“I'm sorry, Yozuki.”

“Eh? What are you apologizing for?”

“Because I told you to give me a minute.” She untied her ponytail and ruffled her head. “But I'm sorry. I didn't need a minute.”

Yozuki looked down at her watch. It had been less than 20 seconds. That was significantly shorter than a minute.

“How did I not notice something so simple?”

Mitsumura's voice held a hint of self-mockery. Yozuki had to ask. 

“What do you mean?”

Mitsumura nodded.

“This locked room has been broken.”

After leaving Mitsumura and the others in the library, I went back to Ms. Breakfast's cottage. I made it most of the way back without running into anyone else, but as I made my way along the beach, I saw Sotodomari. She was munching on a sausage so enthusiastically her snow white twintails swayed. Every time I saw that girl, she was eating something... As I thought that, Sotodomari noticed me and waved at me. Then she approached and struck up a casual conversation.

“I hear there was another murder.”

That was a heavy topic to bring up so casually.

“Yeah, it happened last night,” I said, nodding. “By the way, who did you hear that from?”

“It was Otomigawara. She came by a while ago and reported the latest goings on to me, looking quite pleased.”

“That woman...”

She had no sense of morals, in a bad sense. Well, not like it was possible to have no sense of morals in a good sense.

Sotodomari took a bite of her sausage and asked me.

“So? What's the status of the investigation?”

“Unfortunately, it doesn't look good.”

“Oh? Don't you have Shitsuri Mitsumura with you? If that woman is here, the investigation should be resolved in a flash.”

“Yeah, about that... Mitsumura and I have kinda split up.”

I told Sotodomari about the investigation thus far and how Mitsumura and I were acting separately. She gave me a mysterious smile.

“Oh my, good sir. She's placed such high expectations upon you.”

“She has?”

“Of course. The locked basement and the Decapitation Chamber – wasn't Shitsuri Mitsumura able to solve them both in a flash? If that's the case, she should be able to solve this locked cottage in no time at all. At the very least, it will be faster than asking you to do it.”

“Well... Yeah.”

It was sad, but that's how it was.

“But Shitsuri Mitsumura purposefully decided to leave this mystery to you, even though it would have been more efficient to handle everything herself. What would you call that, if not expectation?”

“Abandonment?”

“Indeed.”

Sotodomari burst into laughter. Then she looked me square in the eyes.

“Well, do your best to live up to her expectations. That's the only way you'll ever stand alongside her.”

I shook my head at that.

“I've never wanted to stand next to her, and I'm sure I never will.”

Because I don't want to stand alongside her. All I want is...

Sotodomari looked at me intently. Then she made a mysterious request. “Hey, show me your forehead.”

I looked at her suspiciously.

“Eh, why my forehead?”

“Just do it!”

I reluctantly brushed my bangs up and exposed my forehead. Sotodomari brought her face close to mine. Then she brought her fingertips up...

“Ha!”

And flicked me square in the forehead.

I writhed in pain. Then I turned an angry glare on her.

“...Why?”

“That was a flick of spirit.”

“A flick of spirit.”

“So, are you feeling spirited?”

“At least I'm not sleepy anymore.”

“Were you sleepy before?”

I gently stroked my flicked forehead. It hurt so bad, and I was annoyed. But, upsettingly, I did feel a bit more fired up.

So I told her.

“I need to get back to the investigation. For some reason, I feel like solving that locked room mystery.”

On my way back to the cottage after leaving Sotodomari, I decided to take a shortcut through the forest. It looked like an animal's trail, but it was surprisingly easy to follow. As I hurried along, I noticed a presence behind me. I reflexively tried to turn around, but before I could, I felt a shock and severe pain in my head.

Apparently, someone had hit me.

The moment that thought crossed my mind, I lost consciousness.

When I woke up, I was lying on a bed, staring at an unfamiliar ceiling. It looked like a room in the mansion rather than a cottage. I guessed it was one of the spare rooms.

Someone noticed me awaken and asked “Are you okay now?” from next to the bed. When I looked over, I saw Mitsumura sitting in a chair, flipping through a paperback book. The title was Murder in the Bronze Age of Locked Rooms.

“Murder in the Bronze Age of Locked Rooms.”

“It's a sequel to Murder in the Silver Age.”

Was that even out yet? After looking at the cover for a while, I scanned my hazy memories. I remembered that someone had hit me and I lost consciousness, but not much else. Had Mitsumura carried me here?

“No, Ms. Hitsujiko did that,” Mitsumura answered my unspoken question. “She found you lying out in the woods. She said it looked like someone had hit you over the head. So she told me about it.”

I see, I think.

“And that's why you were taking care of me?”

Mitsumura looked back down at the paperback. “...It isn't like that. I was just bored.”

And she turned away. Apparently she did have her soft side.

I couldn't help but want to tease her. I grinned and said “Oh, so you were bored.”

“And here I thought you were busy. And here I was, wondering if you'd made any progress on the locked room in the Tower of the Cross.”

“Oh, that?” Mitsumura didn't look up from her book. “I already solved it.”

“Seriously?”

Oh no. She actually did have free time.

I tried to get out of bed with a groan. I felt a sharp, overwhelming pain in the back of my head. I'd been hit harder than I thought. That sucked.

Mitsumura sighed at the sight.

“So, did you see the culprit?”

“No, I don't think so,” I said, trying to remember. “They got me from behind.”

“Useless as ever.”

“Sorry.”

“Well, it's fine. I'm just glad you're alive.” Mitsumura gave a small smile. “It was good for the culprit, too. Because if something had happened to you, I'd have probably killed them myself.”

Mitsumura said that with eyes so cold they froze me in place.

Seeing me like that, she chuckled.

“Just kidding. Were you happy?”

Being told she was going to murder someone actually didn't make me happy.

“But what a relief. And here I thought you'd suddenly become a yandere.”

“I'm not yan, and I'm not dere either. There's no reason I'd ever be dere for you in the first place,” Mitsumura pouted. “Don't be ridiculous.”

Mitsumura sighed before continuing.

“Besides, I don't think the culprit was planning on killing you to begin with. If they had, you would no longer be part of this world.”

I felt a chill down my spine. I raised an eyebrow as I spoke.

“Please don't say scary things.”

“But it's true, isn't it? It's easy to kill someone who's already unconscious. But they didn't. Well, it's possible that someone passed nearby and they quickly fled in a panic, but most likely they didn't intend to kill you.”

I nodded. That was probably the case.

Afterwards, Mitsumura asked me what happened leading up to the culprit's attack on me. It felt like I was being interrogated, somehow. As I traced back my memory, I explained everything that had happened between when I left the mansion and when I encountered the culprit in the forest.

When Mitsumura'd heard my whole story, she hummed for a second, then asked me something.

“Was anything stolen?”

“Stolen?”

“Just a hunch. That's the first thing that comes to mind as a reason someone would attack you.”

I see, so the theory was that they'd needed something I had.

I sat up on the bed and searched my pockets. I had a handkerchief, a cola-flavored candy, and three key cards. Two were the key cards to my cottage, and the other one was the key to Ms. Breakfast's cottage, the scene of the locked room murder.

“Huh?” I realized something. “I'm short a key card.”

There were two key cards to Ms. Breakfast's cottage, and I was supposed to have both of them. But one was missing. That meant...

“I see, so the culprit stole the card key.”

Mitsumura said that and thought for a moment. Then she said “I get it.”

I tilted my head.

“Get it? What's to get? You mean why the culprit stole the key card?”

“No, that's not it,” Mitsumura said. “I know the locked room trick.”

“Wha!?”

I made a stupid noise. Mitsumura got out of her chair, completely ignoring me.

“Then let's get right to solving this. I'll explain the trick of the locked Tower of the Cross as well as the locked room trick with the key card.”

Mitsumura called her shot and went to leave the room. I hurriedly stopped her and said “Wait a minute!”

“Do you really know the trick to the locked room?”

“Of course,” Mitsumura said. “Who do you think I am?”

Certainly, if it were her...

I bit my lip and staggered out of bed. Mitsumura's eyes went wide and she hurriedly said “Hold on!”

“You should stay in bed. You were hit in the head.”

I shook my head.

“No, there's something I have to do.”

“What could be so important?”

“I've made up my mind. I'll solve this locked room.”

Mitsumura looked shocked. She gave me a worried look.

“Are you really okay? You must have been hit extremely hard. I just said that locked room has already been solved.”

“No, not yet,” I said. “I haven't figured it out yet.”

“But-”

“I want to solve it for myself.”

Mitsumura's eyes widened slightly. She looked at me seriously.

“Tell me, is there any point to that?”

I shrugged slightly.

“Oh, I know it probably doesn't mean anything.” I understood. It was completely for my own self-satisfaction. But...

“But I want to solve it myself. Even if it is just a self-satisfying act. Because...”

Because that was the locked room she'd trusted me with. Because it was the locked room she'd told me “try to solve this.”

That meant it was my locked room. Even if someone else already had the answer, it was my locked room, and I had no intention of handing it over to anyone else.

Of course, I could never say something like that out loud.

I remembered what had happened in the literature club room in January at the beginning of the year.

I'd set out to solve the mystery of Japan's first locked room case, which Mitsumura was said to have committed three years ago. I'd presented the trick I'd come up with to Mitsumura. However, Mitsumura easily denied it. She said “I'm afraid you're wrong,” and that was that.

I was completely defeated.

I couldn't help but be happy.

Why wouldn't I be? There was no way I could figure out the trick Shitsuri Mitsumura came up with so easily. I'd probably need the rest of my life and the next to solve it.

Earlier, Sotodomari had asked me if I didn't want to stand alongside Mitsumura. She said some funny things. Stand alongside her? I never wanted something like that.

I wanted to beat her.

I couldn't wait to see what was on the other side of that locked door. Someday, I'll win. Someday, I'll break it down. That's what Shitsuri Mitsumura was to me.

That's why now was no time to be struggling with the locked cottage in front of me.

I'll solve it... I'll definitely solve it. I will never give up.

“......”

I don't know if she could sense my thoughts, but Mitsumura let out a small sigh and said “I understand.”

“It can't be helped. I'll leave the locked cottage to Kuzushiro.” Mitsumura looked like I was forcing her hand, but somehow, she seemed happy. “However, I don't want to spend too much time on this, so let's set a time limit. I'll give you three hours. Use that time to solve the mystery. If you exceed that limit by even a second... I'll end this locked room.”

“That's enough.”

I was sure, three hours was enough.

Then I calmed down and started begging.

“No, actually, it might not be enough. Could you make it four?”

“Eh, I don't want to.”

“Then three hours and 30 minutes.”

“What's the point of 30 minutes?”

Mitsumura sighed and tried to leave the room. But as if she had a sudden whim, she stopped and turned around.

“Let me give you a special hint.”

“A hint?”

“Yes, a hint to the locked room. The hint is this:” Mitsumura said. “Why did the culprit steal the key card from Kuzushiro?”

“So we only have three hours so solve this locked room murder.”

I returned to Ms. Breakfast's cottage and reported to Ms. Chiyori. She looked at me with astonishment.

“How did something like that happen? Explain yourself.”

I had no choice but to tell her what had happened, from when I was attacked by someone to the key card being stolen, and how I'd promised Mitsumura I'd unlock the locked room within three hours. Ms. Chiyori held her head in her hands and said “Oh, why did you agree to that?”

“You've promised something completely unreasonable. Do you really think you can solve it in three hours?”

“It'll be fine, Mitsumura solved it in five seconds. So I'm sure three hours is plenty of time.”

“I really don't think you should be using that girl as a benchmark for anything...”

Ms. Chiyori let out a sigh. To cheer her up, I told her the good news.

“It's alright, I got a hint to the solution.”

“A hint?”

“Yeah, Mitsumura told me. The hint is 'Why did the culprit steal the key card?'”

When she heard that, Ms. Chiyori said “Well, that's easy.” It seemed she'd gotten something from the hint. So I asked her.

“What do you mean?'

“What? You mean you don't get it?”

Ms. Chiyori looked at me in shock. She scratched her head and answered.

“Think about it, Kasumi. The only reason the culprit would have stolen the key card you had is because it was a fake. In other words, one of the key cards the culprit left at the scene of the crime was a fake. That's why they attached you, to collect the fake card.”

“I see.”

That sounded right to me. If I'd kept the fake key card on me the whole time, when the police arrived and investigated, they would have immediately realized the card was a fake. That would be bad for the culprit.

But even though I was convinced, Ms. Chiyori had a troubled look. When she “Hmm”ed in though, I asked her about it.

“What is it?”

“I was just thinking about what Shitsuri Mitsumura said. 'Why did the culprit steal the key card?' That's what she said, right?”

Hearing that just confused me more.

“What do you mean? You said it yourself, it was to collect the fake key card.”

“No, think about it,” Ms. Chiyori said, scratching her head. “Let's assume the culprit did leave a fake key card at the crime scene. So, where did the real key card go?”

Where the real key card went?

“Didn't the culprit just take it with them after killing Ms. Breakfast?”

“Right, they must have. That was the only way they could lock the door to the crime scene.”

That was the only conclusion. I didn't see any problems.

“No, there's a huge problem,” Ms. Chiyori said.

“Huh? What?”

“Think. The culprit knocked you unconscious and stole your key card, right?”

“Right.”

“And since the culprit took the real key card from the scene when they killed Ms. Breakfast, it goes without saying they had the real card in their possession at the time. But that begs the question. Why did the culprit steal the fake key card after hitting you? No, that's not quite it. Why did the culprit ONLY steal the key card? If I were in their position, I wouldn't have just stolen the key card. I would have put the real key card back in your pocket at the same time. That way, you would have had the same number of cards on you as when you were knocked out, and you wouldn't have noticed the switch. You never would have suspected the culprit stole the fake key card.”

I started in shock.

She was right, I had realized the key card had been stolen because one of the key cards I held was missing. If I'd still had two key cards in my possession, I wouldn't have considered the possibility that one of them had been swapped.

“And yet the person who attacked you decided to just take the key card away without replacing it,” Ms. Chiyori said. “Why?”

“Why?”

Of course, I didn't know that. I thought about Mitsumura's hint again.

“Why did the culprit steal the key card?”

The hint she'd given me... I finally realized just how important it was.

The hint could also be interpreted as “Why did the culprit steal the key card without replacing it?” And I thought that solving that whydunit would be the key to unlocking this locked room.

I focused on the issue at hand.

“The most obvious answer would be that the culprit no longer had the real key card in their possession, wouldn't it?”

The culprit didn't have the real key card. Therefore, they couldn't exchange the real key card – that was the conclusion you'd come to if you thought about it normally.

“But is that really possible?” Ms. Chiyori asked skeptically. “The culprit used that key card to lock the door, right? That's for certain. If it wasn't, there's no way they'd be able to lock the room. And yet, the culprit lost that all important key card. Is that even possible?”

She was right. It was inconceivable the culprit behind all these locked rooms would be so foolish as to lost the real key card.

“Besides, there's an even more important problem,” Ms. Chiyori said. “Both of the key cards left at the crime scene were genuine. Because when Ms. Breakfast's body was discovered, you confirmed it yourself, Kasumi. You inserted both the key cards into the card reader on the door and confirmed that they both locked the door – in other words, that they were the two real key cards.”

That was true. I remembered that, and I found the case even more troubling. I'd realized something incredibly strange. “No, wait,” I said. What on Earth did this mean? Because...

“The reason the culprit stole the key card from me was because they left a fake key card at the scene of Ms. Breakfast's murder, right?”

Ms. Chiyori nodded at me and said “Yeah, that's right.”

“I can't think of any other reason.”

“But both of the key cards left at the scene were real.”

“That's definitely true.”

“But isn't that a contradiction?”

The culprit had left a fake key card at the crime scene, but both of the key cards left at the crime scene were real. Could both of those things be true at once? It was a paradox.

“That's true,” Ms. Chiyori said, scratching her head. “But if you think about it logically, they're both true. But that can't be. I'm sure one of our premises is wrong. We've just been made to believe it's true.”

In other words...

① Both of the key cards left at the scene of the murder of Ms. Breakfast are real.

② The key card the culprit stole from Kasumi Kuzushiro is fake.

One of those two premises was wrong, but through some trick, we were made to believe they were both true.

And until we figured out that trick, this locked room would never be unlocked.

“Humph.”

I flopped down on the floor with a groan. Seeing that, Ms. Chiyori panicked and said “What is it? What's wrong?”

I spoke without getting up from the floor.

“You see it all the time in mystery dramas, don't you? I'm putting myself in the victim's shoes. I love it when that happens, so I thought I'd try it and see if I come up with something.”

Ms. Chiyori laughed a bit.

“Unfortunately, I don't think there's any point in doing that here. After all, the victim has no idea what trick was used in this case.”

She was probably right.

As I thought that, Ms. Chiyori also crouched down on the floor and rolled onto her back. When I saw her do that, I couldn't suppress a smile.

“You're doing it too, Ms. Chiyori?”

“Well, it always helps to get a change of perspective.”

We both lay there on the floor in silence for a while, staring at the ceiling. Time passed. The deadline Mitsumura had given us was three hours, but how much time did we have left? Wondering that, I occasionally checked my watch.

I took one of the key cards from my pocket. It was one of the key cards to the cottage where the crime had taken place. I tried holding it up to the ceiling light.

It was really thick for a key card. Most of this insertion type key cards are extremely thin, but this one was about 2mm thick. It was twice as thick as a credit card. That really was too thick.

Did the culprit somehow take advantage of that thickness?

It was about five minutes before the three hour time limit I had promised Mitsumura that I came up with the idea.

When I returned to the mansion, I quickly found Mitsumura. She looked up at me from over the paperback book she was reading.

“Did you solve the mystery?”

“Yes,” I nodded.

Mitsumura smiled at me.

“Alright then. Let's start the deduction show.”

 

 

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