Chapter 5: A True Locked Room

Yashiro had achieved enlightenment. During the two days he'd spent wandering the forest trying to find his way down the mountain, all unnecessary emotions had been stripped from him. All his desires, even his attachments to life. He'd originally been a con artist, and he'd earned the resentment of many people. So now, he could peacefully accept that this day was always going to come.

Yashiro looked up at the other person with fading consciousness. He was lying on his back on the floor with a knife in his chest. He tried to call for help, but he couldn't make a sound. But he felt strangely calm. Even his pain and the suffocating agony, he could accept as his just punishment.

However, there was still one thing he wanted to ask. So, somehow, he found the energy to use his voice and asked the person who stabbed him. He just wanted to know why he was killed... Who had he hurt, what had happened to them, and how had it come back around to find him?

However, the other person didn't have a good answer for him. They did hold a grudge, but now, it somehow felt like it didn't matter anymore.

If they were forced to name a motivation...

“Because I want to make a locked room.”

What...? Those words dragged Yashiro's mind back from the shores of enlightenment. It was as though he'd suddenly woken up and found himself back in reality. Before he knew it, his desires and his attachments to life had returned to him.

He didn't want to die... If he had to die anyway, he at least wanted it to be for a better reason than that. No, he didn't want to die! There was still so much he had to...

At that moment, Yashiro's consciousness faded away.

In the room where the number of living people had decreased from two to one, the person who'd stabbed Yashiro delivered a soliloquy.

“Now then, let's create a locked room.”

It was decided that Riria would be kept confined in a room in the east building. The room that Miss Meirozaka showed me didn't have any sort of thumb turn on the inside, and could only be locked or unlocked with a special key. In other words, it was a perfect room to imprison someone in. It had no windows, and the door was too strong to be broken. The east building didn't have a master key, so there was only one key to unlock it.

“Alright, please step inside.”

“'Ka~ay.”

At Mitsumura's urging, Riria entered the room after a simple body check. After confirming that she was inside, Miss Meirozaka locked the door. She handed the key to Mitsumura.

“Me?”

“Yeah, you seem like the most trustworthy person in the hotel.”

Apparently, Miss Meirozaka didn't know that Mitsumura had been arrested on suspicion of locked room murder in the past. Well, her real name had been kept out of the news, so that applied to most people.

Mitsumura quietly took the key and put it in her pocket.

I fell asleep, and was awoken by the sound of a bell. It was an alarm clock. However, it wasn't the alarm clock in my room. When I checked my smartphone, the time was 2:00 A.M. I opened the door and left the room.

The sound of the bell was even louder out in the hall. It was far louder than a typical alarm clock. The bell seemed to be coming from the third floor of the west building, one floor above me.

Hurrying up to the third floor, I found people already gathered there. Yozuki, Mitsumura, Fenrir, Dr. Ishikawa, and Miss Meirozaka. Everyone except Yashiro and Riria were gathered in front of the door. Including me, there were six people in all. Everyone who was here now had been in the west building already, so they gathered quickly. Riria was being detained, but was Yashiro sleeping soundly through this due to the fatigue from his journey? 

I took another look around the third floor hallway.

I'd heard that the west building was three stories high, but this was actually my first time on the third floor. The length of the hallway was the same as the first and second floors, but the number of doors was different. There were five doors each on the first and second floors, but only one on the third. The number of rooms was different. There were five rooms on the first and second floors, but only one on the third floor, and that room was probably the size of five normal rooms. It seemed like a pretty special room.

“What is this room?” I asked, pointing in the direction the bell's ringing was coming from.

“The library,” Miss Meirozaka answered. “It mainly houses Byakuya Yukishiro's works and his favorite books. Well, there aren't actually that many books there.”

I let out a “Hmm.” Why was there an alarm clock going off inside the library? After thinking about it for a while, I realized that there was no reason to think about it. So...

“Let's just go inside,” I said. “Maybe something's going on in there.”

Mitsumura shook her head.

“We can't go inside.”

“Why not?”

“Because it's locked.”

“Locked?” I had a bad feeling about this. I asked Miss Meirozaka “What about the master key? All the doors in the west building can be opened with the master key, right? Or is this library an exception?”

“No, the library can be opened with the master key,” Miss Meirozaka mumbled. She averted her eyes as though ashamed of a blunder and said “I can't find the master key.”

“Eh? What do you mean?”

“It was hanging in a key locker behind the front desk in the lobby – the locker had a five digit combination. However, someone broke into the locker and took the master key. It was a mistake on my part. I had kept it on my person at all times until yesterday, but after the case was solved, I got careless. I didn't consider the possibility that the locker itself would be broken.”

Things were getting ominous. I turned my attention back to the door the alarm was coming from. Considering the circumstances, it seemed likely what was going on in that room was more than a mere alarm clock going off.

“Even if you don't have the master key,” Yozuki said, “can't we just unlock it using the library key?”

“No, we can't do that either,” Miss Meirozaka said, shaking her head. “The library doesn't have its own key. It's not that the key was lost or broken, it never existed to begin with. Even back when Byakuya Yukishiro owned this building, he made use of the guest rooms, so he had to hand out room keys to his guests, but there was never any need to do that for the library. He could make due with just the master key, so there was no reason to create an extra key.”

We all groaned. In other words, the library door could only be unlocked with the master key – and since someone had stolen said master key, there was no way to unlock the door.

In that case, the only way to enter the room was to break down the door, or...

“There's a window over there,” Miss Meirozaka said, pointing to the end of the hall. At the end, on our left, was a window into the library. The window was made of frosted glass, so we couldn't see what was going on inside. We couldn't see anything except that the light in the room was on.

“I'll get a mop,” Miss Meirozaka said before going downstairs. She returned a few minutes later, mop in hand.

“Get out of the way,” Mitsumura said as she took hold of the mop. We all did as we were told, and Mitsumura took a step back from the window and jabbed at the glass with the tip of the mop handle until there was an opening big enough for a person to pass through. Then she climbed over the window frame and entered the room. I followed after her. The alarm clock had been placed right next to the window, so I turned it off before looking around the room.

It was a very spacious room, made by connecting five rooms' worth of space. All the bookshelves were placed against the wall opposite the hallway side, and there were only a few chairs filling the empty space of the room. A locked room with a wonderful view and no blind spots. That was how I immediately saw the person lying in the center of the room. It was Yashiro. There was an immediate turmoil among our group. His eyes were wide open, and it was clear he was dead.

“This is...” Mitsumura ran up next to Yashiro and picked up the bottle that had been placed at his side. It was a large bottle with a screw-on lid. Inside the sealed bottle was a key.

“It's the master key to the west wing,” Miss Meirozaka said. “No doubt about it.”

“Is that so?”

In other words, the only key that could lock the library had been found inside the library.

Mitsumura let out a soft “Hmm,” before approaching the door to the room, still holding the bottled key. Then she let out a rare surprised voice that said “No way.” When I approached to see what was going on, I saw why. The thumb turn of the door was set to the locked position, and it was clear the door was actually locked. I turned the doorknob, just to be sure. It was really locked. That meant there was no way the culprit could have left the room through the door. The window, which we'd had to break through to get in, was also locked. Therefore, there was no way the culprit could have entered or exited the room.

It was a perfect locked room – but that wasn't that surprising. Even before we'd broken the window, we'd all expected to some extent that this would be a locked room.

The real problem was something entirely different. The thumb turn used to lock the door from the inside was covered in a dome of transparent plastic.

“This is...” I said.

“It's a gachapon capsule.” said Mitsumura.

It was the lid of a capsule toy from a gachapon machine. It had been placed directly over the thumb turn, preventing us from touching it directly.

Mitsumura tapped the lid of the gachapon capsule with her fingernail. Then, she murmured an amused “They're challenging me.”

“You think they did this to erase a common locked room trick category?”

I nodded at her. “It's likely,” I said.

“Like this, they couldn't have turned the thumb turn to lock the door.”

One of the classic locked room solutions is to use some sort of mechanical device to turn the thumb turn from inside the room. But this wouldn't let us do that. The lid of the capsule was firmly affixed to the door with cellophane tape, and it had clearly been attached by hand. After turning the thumb turn with a mechanical device, the gachapon was attached using another mechanical device... No matter how you looked at it, it would be impossible. No, to begin with, mechanical devices inevitably leave remnants at the scene. And the number one way to recover traces is...

“Impossible,” Mitsumura said as I went to look under the door. “There's no gap under the door, so they couldn't have retrieved anything through it.”

The door was the same as the ones of all the guest rooms in the west wing, a single, solid chocolate bar with a doorknob. Like in my room, there was no gap under the door, making it impossible to retrieve anything through it. In the first place, it was already impossible to turn the thumb turn due to the gachapon, and now it was even more impossible to retrieve the evidence.

“Besides that, there aren't any blind spots in the room,” said Mitsumura, who was still holding the bottled key. “That means the culprit couldn't have been hiding inside the room, either.”

After being told that, I looked around the room. All the bookshelves were against the wall, and the only furniture was simple chairs. The chairs themselves were simple wooden frames, so it was impossible for anyone to hide behind one. In that case, tricks in the “pretend the culprit had escaped from the room when they were actually still hiding inside” family were off the table. Well, all six people other than the imprisoned Riria were already seen outside the library, so that possibility had been rejected from the beginning.

“Then all that's left is,” Mitsumura shook the bottle she was holding. The key rattled around inside the glass, making a metallic sound. “The possibility that this key is a fake.”

Mitsumura twisted the lid of the bottle and tried to open it. But it appeared to be sealed tight and it wouldn't open. She pouted her lips and handed the bottle to me. I took the bottle and twisted the lid. It was definitely on tight. Unreasonably tight. It took blood, sweat, and tears, but I eventually managed to open it.

After Mitsumura confirmed I'd done it, she removed the cellophane tape from the gachapon capsule over the thumb turn. The tape peeled off. However, the end of the tape tore, and a 5 mm piece was left stuck to the door. Mitsumura scraped at it with her nails, trying to get it off, but she eventually gave up and just unlocked the door, letting us step into the hallway.

“Kuzushiro, the master key.”

I took the master key from the bottle and gave it to Mitsumura. She inserted it into the keyhole and turned it. I heard the door lock. I rattled the knob, but it was perfectly locked.

“It looks like this key is real. In other words, the only key that can lock the library was found inside the library after all.”

At that point, we had proven that the crime scene was a perfect locked room.

Mitsumura inserted the master key back into the keyhole, unlocked the door, and entered the room. She asked a question to Dr. Ishikawa and Fenrir, who were conducting the autopsy.

“What is the estimated time of death?”

“About two hours ago,” said Dr. Ishikawa. “It's after 2:00 A.M. now, so I'd say around midnight.”

“And the cause of death?”

“He was stabbed. He was stabbed several times in the chest, but most of them appear to have been inflicted postmortem. No vital reactions. Also, judging by the amount of blood on the floor, he was killed somewhere else and moved here. And the murder weapon hasn't been found.”

“So it wasn't a suicide.”

“Because he was stabbed after death. Also, Miss Fenrir?”

Ishikawa turned to Fenrir. She nodded and showed Mitsumura something.

“This was found in the corpse's pocket.”

It was a playing card. The nine of hearts, clearly from the same set used in the Playing Card Serial Murder Case.

“So the card's number is nine,” said Yozuki, who'd come closer. “If we apply the Ten Commandments, does that mean he bore false witness?”

“Come to think of it, Mr. Yashiro had conned people,” I said. “It fits.”

“Yes, but I think there was another reason the culprit left this card at the crime scene.”

I tilted my head at Mitsumura's words. But before I could ask what she meant, Dr. Ishikawa said “More importantly...”

“Why did another murder happen at all? The case was solved, right?”

“Yes, it was,” said Mitsumura. “Even after it was solved, another incident took place. That means a second culprit appeared after we caught Miss Riria.”

Dr. Ishikawa muttered a “Seriously?” Then, scratching his head and never letting up that smile, he said “Isn't it possible this was also Miss Riria's doing? Rather than a new culprit suddenly turning up, it makes more sense to assume Miss Riria just killed another person.”

Mitsumura shook her head before responding.

“It's impossible that Miss Riria is the culprit. She's been confined to a room in the east building, and I have the only key to the room, so it's impossible for her to have come here to kill Mr. Yashiro. But... If it would set your mind at ease, we could go check on her.”

We headed to the room in the east building where Riria was being held. Mitsumura unlocked the door and turned on the lights. “...What is it?” Riria asked, rubbing her eyes.

“...She's still here.” Mitsumura turned to look at Dr. Ishikawa.

“Ah, so she is,” Dr. Ishikawa nodded.

“...What are you talking about?” Riria looked confused. Mitsumura said “I'll explain tomorrow,” and shut the door to Riria's room.

“So,” we resumed talking after the door was locked. “Miss Riria wasn't the culprit after all,” Fenrir said. Mitsumura nodded.

“I didn't suspect Miss Riria of the murder from the beginning.”

“Why not?”

“The locked room was too strong,” Mitsumura said in response to Fenrir's question. “We haven't fully investigated yet, but it's clearly on a different level from any of the previous cases. The thumb turn was covered by a gachapon capsule, rendering it unusable. The master key, the only key that can lock the door, was found in a bottle with the lid closed tight. And unlike in the first murder that claimed Mr. Kanzaki's life, there was absolutely no gap under the door.”

“It truly is a Complete Locked Room.”

“It might even be the step beyond that... a Super-Complete Locked Room, if you will. If Miss Riria were capable of coming up with a locked room trick of this caliber, I would have had a bit more trouble solving the four locked room murders she did commit.”

She made it sound like she hadn't had any trouble with them. Well, maybe she hadn't. After all, she was a light speed detective clown.

“More importantly than that,” Mitsumura told us, “I would like to investigate Mr. Yashiro's room now. Mr. Yashiro was murdered somewhere else, and his body was moved to the library. In that case, it is likely the real crime scene is his room.”

When we went to Yashiro's room, it was just as Mitsumura had predicted. A pool of blood was on the floor, making it obvious this was the real scene of the crime.

Dr. Ishikawa let out a yawn.

“I'm tired, so I'm turning in for today. ...I'm worried, though. I hadn't expected them to kill off another person at this stage.”

Dr. Ishikawa made complaints like that. Yozuki nodded sympathetically.

Afterwards, we returned to the library and brought Yashiro's corpse down to the wine cellar. The wine cellar with five corpses had fully become a morgue.

After saying goodbye to the others, Mitsumura and I decided to return to the library and investigate the locked room. When we opened the door to enter the room, something came to mind. I told Mitsumura.

“Is it possible the culprit removed the door by unscrewing the hinges?”

That was also a classic trick. After going out into the hall, the culprit unscrewed the hinges and removed the door. Then, after turning the thumb turn to make the deadbolt stick out, they carefully fit the door back in the frame and reapplied the screws to secure the door. That was a known trick.

When I asked her about it, Mitsumura looked at me in astonishment and asked “Kuzushiro, did you come from the Golden Age?” I think she meant it as an insult, but it didn't sound like one. After all, the term “Golden Age” referred to the era when Agatha Christie and Ellery Queen were active as writers, and legitimate mysteries were at the height of their global popularity.

Not only that–

“Focus, Kuzushiro,” Mitsumura admonished me. “There's no way a trick like that could be used in this day and age. You can tell at a glance; just look at the door. Well, Kuzushiro? Where are the screws on the door hinges?”

“Um...” I did as I was told and looked for the screws. They were on the sides of both the door and the door frame.

“They're here, on the sides,” I reported.

“Okay, now try closing the door.”

I obediently shut the door. And I went “Ah.” When the door was closed, the screws of the hinges were completely hidden. There were screws on the side of the door and on the side of the door frame. When the door was closed, those sides touched, so the screws were trapped between the two.

“And how do you plan to reattach the screws like this?”

Come to think of it, that was true. But it was strange. I'd heard of the “remove the screws and reapply them from the outside” trick dozens of times. How could it have actually been impossible?

“I don't know much about it, but I believe old doors had a different design.” Mitsumura said. “One that didn't hide the screws when the door was closed, but left them exposed on the outside. If the door opened outwards, it would have that structure, wouldn't it?”

“I see,” I thought. “In that case, it would be possible to remove and reattach screws from the hinges even with the door closed.”

But thinking about it logically, that was dangerous. If the screws were exposed from the outside of the room, that meant the door could be easily removed. And that meant that thieves could freely enter.

“Actually, in the past, that was a common method used by thieves,” Mitsumura said. “The trick you mentioned was apparently inspired by thieves' methods. But as I just explained, it can't be used in modern times.”

I reopened the door with a grunt and looked at the hinges.

“But I really do feel like there's a screw loose here.”

“It's just your imagination.”

Mitsumura was getting upset with me. Then she entered the library, approached a wall, and began to touch it. “What are you doing?” I asked. “I'm checking to see if the culprit made a hole in the walls of the room,” she replied. If the culprit had secretly drilled a hole in the wall and used it for a trick, that would significantly weaken the locked room. That was the possibility she'd chosen to investigate.

Mitsumura and I investigated together for about an hour, but we didn't find a single hole in the walls or ceiling. “There doesn't appear to be one,” Mitsumura concluded. She rubbed her eyes sleepily. It was almost four in the morning.

“Let's take a break for today. We'll continue tomorrow.”

Mitsumura said so and started to leave the room. I went to follow her, but I suddenly remembered something and stopped her.

“What is it?” Mitsumura said brusquely. She looked tired. I ignored her tiredness and asked.

“You said earlier that the card left at the scene had another meaning.”

The number nine playing card left at the scene was a reference to the ninth commandment, “You shall not bear false witness against your neighbor.” Since Yashiro was a former conman, he definitely fit the bill, but Mitsumura had said earlier that the culprit left it for another reason.

“Ah.” Mitsumura yawned. “Perhaps the culprit didn't want to pattern the crime after Moses's Ten Commandments, but Knox's?”

“Knox's Ten Commandments?”

“Yes.”

“You mean this crime represents Knox's ninth?”

I traced my memory. Knox's ninth commandment was the one forbidding the Watson from concealing any thoughts they had. I raised my eyebrows in confusion. What did that mean? How did that connect to Yashiro?

“Was he a Watson?” I asked. Mitsumura shrugged and said “Well, he may have been an assistant at some detective agency in the past.” It was an appropriate remark.

When I looked at her in dissatisfaction, Mitsumura said “Kuzushiro. What's your interpretation of Knox's ninth commandment? In other words, what rule does it impose on the mystery writer?”

I thought about it for a while.

“It's the spirit of fair play.”

“Of course, that's true, but I also interpret it like this:”

Mitsumura stroked her black hair.

“It's a complete denial of narrative tricks.”

I frowned at her unexpected declaration. What was this girl talking about? Originally, Knox's ninth was supposed to forbid the Watson from intentionally concealing any information necessary for the reader to make deductions. I, at least, had never heard it called a denial of narrative tricks before.

I couldn't help but ask “What do you mean?”, and she replied “What is a narrative trick, anyway?”

“It's not even worth explaining,” I explained, “but a narrative trick is a technique that misleads the reader's perception through purely textual devices. A typical example would be the use of selective language to mislead the reader into thinking a female character is male.”

“The classic gender misdirection trick. So, how does the misunderstanding come about?”

I tilted my head this way and that, then answered.

“Because the author used literary devices.”

“Of course, that's true, but more fundamentally. Why does the trick exist?”

“Because the author wanted it there.”

“I don't mean like that,” Mitsumura sighed. “The answer is that the author intentionally withheld the information. The author concealed the gender of Character A. Otherwise, the reader wouldn't have misunderstood A's gender. And if the author is intentionally withholding information, it means the point of view character, the Watson, isn't conveying that information to the reader.”

I see, I think. It's true that the Watson could clearly see the gender of the person in front of them. But the Watson didn't tell the reader that. That's why the reader misunderstood. That's what she was getting at.

But that raised another question.

“Why did the killer leave the number nine at the crime scene?” I understood that Knox's ninth could be interpreted as a rejection of narrative tricks or whatever, but I didn't see what the killer was saying it for.

“Exactly how it sounds,” Mitsumura said, raising her index finger. “There are no narrative tricks in this locked room. The culprit wanted us to understand that, so they left the number nine in this room.”

I had no idea what she was saying. That might have been the most unintelligible thing she'd said since we met.

“No, hold on, what are you saying?” I asked, brow furrowed deep. “There's no connection between locked rooms and narrative tricks.”

Mitsumura looked at me like I was an idiot. She stared deep into my soul.

“Everyone who likes mysteries has thought of the possibility of using narrative to create new locked room tricks at least once. So I assumed you had, too, Kuzushiro.”

“I've never given it any thought.”

“So, you don't actually like mysteries, Kuzushiro?”

My love of mysteries was denied. That hurt, Mitsumura. That hurt me deep.

I coughed.

“Narrative tricks suck, anyway. They're the domain of amateur hacks who don't know what they're doing. Real connoisseurs enjoy physical tricks and the logic that leads to the culprit.”

“Wow. So that's the sort of person you are. I think narrative tricks are amazing. They're so flexible, you can use them in any sort of novel. They fit in with any genre: Romance, comedy, sci-fi, fantasy, horror... But physical tricks aren't like that. The moment you break out the needle and thread, you've trapped yourself in mystery.”

“Can we get back on topic?” I cut her off. “I still don't understand the idea of creating a locked room with a narrative trick in the first place. Is something like that really possible?”

“Well, for example...” Mitsumura paused for about ten seconds. “Okay, here's one I just came up with. Ready?”

“Shoot.”

“Okay, so: A murder occurred in a certain room. The crime scene had a door and a window, but both were locked. So, how did the culprit escape the room?”

There were too few clues. I gave it a minute's thought, then said,

“Tell me.”

“The answer is, the glass of the window was broken. The window was locked, but there was a hole in it. The culprit escaped through the hole.”

That was a terrible answer. Naturally, I objected.

“No, that isn't a locked room at all.”

“Of course it isn't. I never said otherwise. That was just your misunderstanding, wasn't it?”

I thought back to the problem Mitsumura had posed. She never did use the words “Locked Room”. She said the doors and windows were locked, but that wasn't the same thing.

“This is how you create a locked room using narrative tricks,” Mitsumura said. “By withholding necessary information, you mislead the reader. Well, the example I just used is a bottom-tier trick. If anyone actually used it, the readers would get angry. Another example would be to use a narrative trick to make the culprit in the room 'invisible'.”

Make the culprit “invisible”?

“You mean the culprit was still in the room, but since they were invisible to the reader, they'd misunderstand that the culprit disappeared from the locked room?”

“Yes, something like that. There was a cat in the room, but the cat was actually a human. The ol' 'human-cat mix-up switcheroo' trick. Well, that's not a good trick, either, but... Do you get it? This is how you create a locked room using narrative tricks. And by leaving a nine at the scene, the murderer erased the possibility of narrative tricks. They declared that this locked room wasn't a narrative trick, but a physical trick – or a psychological one. In a sense, it's a statement of intent. This locked room is completely fair – no unfair moves used. That must be what they were saying, right?”

I was extremely confused.

“Just who is the killer talking to here?”

“Oh? You mean you can't tell?”

Mitsumura stifled a yawn.

“I'm tired, so I'm going to bed now. Good night.”

I replied “Good night.” She stepped out of the library with a smile on her face.

The next morning, Mitsumura and I went to the room in the east building where Riria was being held. When I told her that another murder had occurred, her eyes went wide and she spoke in a disappointed voice.

“I can't believe you all were out having fun without me.”

“We're all really confused about it,” Mitsumura said.
“So? What's up? Did you come to ask the Great Detective Riria to help with her great deductions?”

“No, I can handle that part myself. Rather...”

Mitsumura rummaged through her pocket and pulled out a playing card. It was the nine of hearts found at the scene. She showed it to Riria.

“Is this your card, Miss Riria?”

Riria looked intensely at the card. And she nodded.

“Yeah, it is. Was this left at the scene?”

“Yes, so I'd like to know, where did you keep these playing cards? That is to say, how did the culprit get it from you?”

Riria looked from side to side as though she were planning something. But she frowned and shrugged, as though she'd decided it wasn't worth it.

“I'll need my smartphone to explain it.”

“Your smartphone?”

“Yeah, it's on the couch by the window in the lobby, so go get it. I'll explain then.”

Mitsumura and I exchanged a look, but we decided to follow the instructions for now.

As Riria had said, her smartphone was on the couch in the lobby. When we returned to the room and handed it over, I asked “Why did you leave it there, anyway?” “I didn't put it there on purpose,” she said grumpily. “I was playing with it in the lobby when Mitsumura started her deductions, so I forgot it there.”

The edge of Riria's smartphone had a protrusion that resembled the crown of a wristwatch. Riria pinched it with her fingertips and quickly pulled it five times. Then she pushed it in five times. There was a click, and the smartphone's case slid vertically open, exposing a hidden case with space for several playing cards. The eight of hearts was being kept there.

“A card is missing,” Riria said. “Yesterday, the nine of hearts was in here, too.”

“Does that mean the culprit stole it?”

“Looks like it. I did put the nine of hearts in there, and I never took it out or gave it to anyone else.”

Mitsumura “hmm”ed in though, then asked Riria another question.

“Is this phone case available for purchase?”

“Nope! Customer ordered,” Riria said. “I had a friend of mine who's good with gadgets make it for me. Isn't it cool? It's the only one like it in the world.”

“So, you, Miss Riria, and your gadget maker are the only people who know about the secret compartment in your smartphone?”

“Well, my friend knows to keep their mouth shut, so I don't think they'd ever tell anyone about a customer's order. I've never told anyone either – I mean, that'd totally defeat the point, right?”

“And you've never opened this secret compartment in public? You only open it in secluded places?”

Riria nodded.

“Usually, I only open it in my home and stuff like that. Or, like, in my private hotel room or something.”

“And since your arrival here?”

Riria thought for a moment, then spoke.

“...Since I arrived at this hotel, I've only opened it in my room. Like, when it was time to commit a crime, I'd take the right card out in my room before I headed out.”

Mitsumura nodded, then turned to me and said “Let's go.”

“Huh, you're leaving already?” She sounded upset. When Mitsumura said “We're busy,” she suddenly remembered something.

 “Come to think of it, I'd like to investigate your room, Miss Riria. Is that alright?”

“Sure, it's fine. Just don't touch my stuff. Now, you'll need this.”

Riria took something out of her pocket and handed it to Mitsumura. It was a key. However, it wasn't the key to Riria's room in the west building.

“...What is this?” Mitsumura asked.

“It's the key to the extra lock I bought at the home improvement store. It's the type you attach to the doorknob so it doesn't rotate and you can't enter the room. The only way to unlock it is with that key.”

“Hmm, so it's impossible to enter your room without this key...” Mitsumura stared at the key. “...But why go to all this trouble?”

“Because I'm a nationally famous actress,” she said with a straight face. “When you're a Riria-class celebrity, you can't even trust hotel staff. They're all Riria fans, too, so there's a possibility they'll use their master keys to enter my room without my permission. That's why I always keep that lock on me when I travel. Sometimes I keep a knife in my bag, so it'd be a real problem if someone saw.”

Mitsumura nodded, said “I see,” and thought for a moment. Then she said “Thank you,” and left the room. Riria went “Eeeeh, you're leaving already?”, then sat back down, looking extremely bored.

Riria's room was the detached room off the west building. A corridor with walls and a shingled roof extended north from the first floor of the west building, and passing through it, we arrived at her door. Mitsumura unlocked the auxiliary lock with the key she'd received from Riria, and the door itself with the west building's master key. Upon entering the room, Mitsumura immediately went to the window. There was only one window in the room, with heavy curtains. Mitsumura examined it with a thoughtful expression, then softly declared “There's a hole in this.”

When I came closer, I saw there was indeed a hole the size of a human fingertip poked in the curtain. On the other side of the curtain was the closed window. She closed the curtains again.

Then, Mitsumura started to search the room. After about a minute, she exclaimed “There's something here.” She picked up a suspicious device off the table. It looked like half a pair of binoculars. Would that make it one binocular? Or would that be a monocular?

“What is that?” I asked, tilting my head to the side.

“Maybe it's a hidden camera detector.”

“A hidden camera detector?” I'd never heard of a device like that. “Not a bug sweeper?”

Mitsumura gave a gentle shrug.

“It's completely different. When you look through the scope of this device, any hidden cameras in your field of view will begin to flash. When it's on, it emits LED light, which reflect off the lenses of hidden cameras. The detector can see that reflected light. It's like an optical version of sonar. Given the nature of hidden cameras, there can't be anything in between the subject and the lens, so if the camera can see the subject, than the subject can also see the camera. This machine takes advantage of that property. Some of these detectors are so sophisticated that they can detect a pinhole camera from ten meters away.”

After giving her explanation, Mitsumura looked puzzled and said “The question is, why did Miss Riria have a device like this?” That was when I remembered it and said “Oh, that's right.”

“Now that I think about it, Riria had a bug sweeper, too.”

I'd seen it on the first day we arrived at the hotel. When I told Mitsumura about it, she said “That's very interesting.”

After combing her fingers through her dark hair, she turned to look at the window.

“Shall we go out in the garden?”

That was what she suggested.

We moved back to the central building and out the front door. A few centimeters of snow were piled in the garden. It was the snow that had fallen on the first day. It hadn't snowed since then, but it was cold enough that it still hadn't melted. However, the snow wasn't fresh anymore. It had been trampled under all our footprints several times. But when we went north through the garden and arrived at the annex Riria was staying in, we found it completely bare, with nary a footprint to be seen. We circled around, but there were no footprints to be seen. Mitsumura took out her phone and snapped a few pictures. When we finished circling the building, she let out a small gasp.

“That's the window from earlier.”

When I followed her line of sight, I saw that there was, in fact, a window. It was the one window in the room we'd seen earlier. She approached the window, trampling the fresh, untrampled snow. But the window's curtains were closed, so we couldn't see what inside.

“No, look, we can see through here.”

Mitsumura tapped the window glass. When I looked at the area she indicated, I saw a small hole in the curtains. It was the same one we'd seen earlier. The hole was only the size of a fingertip, but if you put your head right up against the glass, you could see through it into the room. The bed and furniture came into view. The field of view was wider than I'd expected; I could see almost the entire room.

When I pulled back, Mitsumura started peering into the hole through the window again. She stayed in that position for several minutes, motionless as a statue. When I said “Oi,” she replied “Just a bit longer.” Was she enjoying herself? Just as I thought that, she quickly moved away from the window. Then she looked at me.

“Let's go see Miss Riria again. I have something I need to ask her.”

“And what would that be?”

“The curtains in that room were closed when we entered the building, right? So I want to know if Miss Riria kept them closed the whole time. I'd also like to know when she closed them to begin with.”

I nodded and said “I see,” but I had no idea why she wanted to know that. With that question still in my head, we returned to Riria.

“When did you close the curtains?” Mitsumura asked Riria. She looked as confused as me. With that uncomprehending look still on her face, she said “I closed them right when I first entered the room, and I haven't opened them since. They've been closed since the first day.”

Mitsumura nodded. She looked at Riria and said “Thank you very much.”

After hearing Riria's story, we went back to the crime scene, the library. Of course, we were aiming to solve the locked room mystery. What caught my attention was the thumb turn on the inside of the door. Even though it was covered by the gachapon capsule, I couldn't shake the feeling it was the key to the locked room.

I started thinking.

If the culprit used this thumb turn to lock the door, there would be four major obstacles standing in their way: ① How did they turn the lock from the outside? ② How was the device used to do so removed – or destroyed? ③ How did they attached the capsule from the outside? ④ How was the device recovered/destroyed?

“.........”

Nope, this was impossible. My head starting hurting immediately.

“I guess I'll just start trying things,” I said to myself as I took some fishing line from my pocket. If you say “locked room”, this stuff is going to come up at some point. However, this door was nearly airtight, and there was no gap between the door and the frame where I could fit my line through There was absolutely no gap where a string could be fit to manipulate things from outside the room. But as I looked at the door, I suddenly thought of a way to pull the string. “Huh?” I went.

“What is it?”

Mitsumura, who had sensitive ears, came over at once. She was a girl who was sensitive to clues. I thought about hiding the information, but in the end, I shared it. “Look,” I said, pointing at the door.

“The piece of tape is missing.”

When Mitsumura had removed the gachapon capsule from the door yesterday, about 5 mm of tape had remained on the door. But now, that scrap was gone. “You're right,” Mitsumura said, leaning her head towards the door.

“That's gotta be the culprit's doing, right?”

“I suppose so.”

Mitsumura agreed with my assessment. It was hard to imagine that piece of tape just coming off on its own. Which only left the possibility that someone had torn it off, and I couldn't think of any reason someone other than the culprit would do something like that.

But what was their goal? Was that piece of tape such an important piece of evidence that the culprit had to make sure they destroyed it?

“Hey, Mitsumura, what do you think?”

“...Uh-huh.”

She gave a totally indifferent reply. She stared at the door and thought for a while, then said “I suppose that was it after all.”

She murmured to herself, then finally looked away from the door. And she turned her eyes towards me.

“Hey, Kuzushiro? I'm sorry.”

Mitsumura said something.

“I'm abandoning this case.”

The noise I let out was ridiculous. I hurriedly started talking.

“Huh, what do you mean? You're just giving up on the case?”

Mitsumura nodded. I was getting more and more confused, and I hesitated to ask.

“Could it be that you've realized you can't solve the mystery?”

“No, it's just the opposite,” Mitsumura said. “It's because the locked room mystery has been solved that I am recusing myself from the case.”

That didn't make sense. If the case was solved, why shouldn't you say so? Shouldn't you just tell everyone the answer?

“Because it would put me in danger.”

Mitsumura's cool eyes sucked the warmth from the room. With a cold expression, she said:

“It's the same.”

Her voice reached my ears.

“The trick in this case is the same one I used in the locked room murder three years ago.”

I was dreaming. It was a dream I'd had in my first year of high school. At that time, I was always thinking about locked rooms. Even when I was at school, or on my way home from school, or even when I arrived home, all I thought about were tricks for the locked room murder Mitsumura had told me she'd committed.

I toyed with all sorts of different possibilities in my mind, and sometimes I tested my ideas on the door of my bedroom. Every day was spent in a locked room. Thinking back, I don't remember the dream all too well.

However, I was definitely with her, in the locked room.

I woke up to the feeling of a hard floor. It was the floor of the library, the scene of the crime. It seemed I'd fallen asleep while lying down and thinking about things. Just as I was about to sit up, I heard a scream. When I turned my head, I saw Yozuki, blue in the face, standing there. She put a hand over her heart and nearly deflated in relief.

“Thank God,” Yozuki said. “I thought you were dead.”

Apparently, I looked like a corpse. Well, I was lying down at a crime scene, so it was an understandable mistake.

As I got up off the floor, Yozuki asked me something.

“How's the investigation going?” she looked around. “Or rather, where is Mitsumura?”

How did I answer that? I avoided meeting Yozuki's eyes as I answered.

“We had a falling out.”

“Eh? Why?”

“We disagreed on our direction.”

“You sound like a band. Ah, I see.”

“What?”

“She dumped you.”

Yozuki nodded as though she understood. Of course, she didn't.

“Anyway,” I said, “she's turned her back on the case. Apparently, she's not involved anymore.”

Hearing that, Yozuki gave another “Huh?”, followed by a “Then what should we do?”

“Kasumi, are you planning to solve the case yourself?”

It was an unexpected question, and I was momentarily taken aback. I quickly shook my head.

“I don't think so. It's too much for me.”

“Yeah, you're right,” Yozuki nodded. “It's too heavy a burden for you.”

“Besides, Mitsumura's brain is too different from mine.”

“Yeah, you're right. You're as different as a cute neighborhood cat and a University of Tokyo student.”

As usual, she had a terrible mouth on her. I was getting a little angry.

“Anyway, I don't plan on involving myself in this case any further. If I can't figure it out no matter how much I think, than I just won't waste my time.”

I told that to Yozuki. “I see,” she murmured, tilting her head to one side.

“But that's a lie.”

“Huh?”

“Kasumi, you're a terrible liar.”

Yozuki smiled at me.

“Because Kasumi, you're itching to solve it, aren't you? You want to solve this locked room mystery more than anything, right?”

I touched a finger to my lips. They'd formed a faint smile.

I asked her, quietly.

“Do I really look like that?”

“Yeah, I can see it. Kasumi, you look like you're having a lot of fun.”

I touched my mouth again. It seemed my true feelings were leaking out. I wasn't Fenrir, so it was a huge breach of ethics to be having fun with the scene of a murder, but I couldn't help the way I felt. In the end, I guess we were the same.

I was having the time of my life.

It was so fun I couldn't stand it.

I'd made up my mind.

Because I could challenge her locked room again.

The locked room trick Mitsumura had used three years ago.

The locked room where the “ultimate trick” she's told me about in the literature club room was used.

“I killed my father”...

The words she'd spoken to me on that summer day a year ago. The words I'd heard from her in an alley dyed the angry red of summer. Ever since that day, I'd been obsessed with the mystery of the locked room she'd left behind. It was like falling in love. That day and every day since, my life has revolved around that locked room.

It was like an adolescent boy becoming addicted to light novels and chuunige.

Or the obsession you felt for your favorite idol group.

Or how you imitated the style and mannerisms of your favorite young musician.

That was me and Shitsuri Mitsumura's locked room. I'd taken on the challenge with all my might. Everything in the world had vanished except for me and that locked room.

Why I was so obsessed... There were many reasons. I could have said I was just curious. I might have been interested in “the ultimate locked room trick”. But there was something more important than all of that...

I just wanted to see the face she'd make.

Mitsumura is a genius. She can do anything. I was amazed by her. But I'm rarely able to surprise her. There have been times she's been dumbfounded by how stupid something I've done is, but I've probably never been able to surprise her by exceeding expectations.

That was why I wanted to see it.

When I imagined that scene, I couldn't help but get so happy that my face relaxed, and for some reason, I also felt a little nervous. So even though I didn't think I'd ever see her again, I was always thinking about that locked room.

Well, in the end, I did give up trying to solve it.

The locked room mystery Mitsumura left was an extremely high wall. As a high school student, it was impossible for me to solve it using only the information I could find in magazines and on the internet.

Alright then...

What if I didn't have to get information from magazines and the web, because I was actually there on the scene?

What would happen? Would I still be unable to solve it? No, I think it would be solvable. Would it? Well, let's try it out. Because lucky me...

There was a locked room right here perfect for testing that hypothesis.

“Thank you, Yozuki.”

“What? What are you thanking me for all of a sudden?”

Yozuki looked confused. 

“I don't understand what you're talking about.”

“...Ah, yeah.”

Obviously. Maybe I'd disappeared a bit too far into my own head.

But thanks to Yozuki, I knew what I wanted to do. So I thanked her again and left the library. With sure steps, I made my way to Mitsumura's room.

When I knocked on the door to her room, Mitsumura immediately appeared. She furrowed her brows in dismay and spoke with undisguised frustration.

“Sorry, but I won't tell you the answer to the locked room.”

She said so and tried to shut the door. I wedged my foot between the door and the door frame. It kinda hurt. She tried to shut the door again. It really hurt. Mitsumura gave up and opened the door. I spoke to her.

“Too bad, I wasn't going to ask you for the answer. There's no need for that.”

Mitsumura looked confused.

“What do you mean?”

“Because I'm going to solve that locked room mystery myself.”

Mitsumura's eyes widened in surprise. Her face quickly turned into a smile.

“Do you really think you can do something like that?”

“I do,” I nodded. “I'm a lot more impressive than you think. I will solve this case. And when you hear my solution, you'll fall to your knees and curse your idiocy.”

Mitsumura was taken aback. She smiled again, but it was strained. “If you don't know what you're doing, you can just say so,” she said mockingly. “There's no way you can ever solve that locked room mystery.”

“No, I can solve it.”

“You can't.”

“I'm going to solve it.”

“It will never be solved.”

She narrowed her cool eyes.

“I know... That mystery will never be solved. Not just by you. There's no one in the world that can solve it. That's the sort of locked room it is.”

I answered her confident words with a shrug. There was no need to be intimidated. Everyone in Japan already knew how hard that locked room was.

So I relaxed, even got a bit smug. “That isn't important,” I said.

“There's something I'm concerned about.”

“Concerned?”

“Yeah, I'm really concerned,” I nodded. Then I pointed at Mitsumura's face. “You were found not guilty of the murder three years ago. Your acquittal stood even before the Supreme Court. Under Japanese law, that verdict can never be overturned. Even if someone solves the locked room mystery, your acquittal is indestructible.”

Retrials in Japan are only held to overturn wrongful convictions or correct other injustices against defendants. A person who has been acquitted of a crime can never be tried again, even if new evidence comes to light.

Mitsumura looked at me dubiously. She hesitantly said “I know that. What about it?”

“So I'm concerned,” I said. “Even if you are legally innocent, the public won't react like that, will they? If the locked room mystery gets solved, you'd get in big trouble. The media would hound you day and night, and the internet would tear you to shreds. You could call it karmic retribution, but I don't want to see you go through something like that.”

She looked ever more skeptical, so I told her about my proposal.

“So if you want, I won't reveal the truth about this locked room trick to the public. It might violate my civic duty, but so be it. I'm okay if the answer remains between just you and me, without letting Yozuki or anyone else know.”

That was my way of showing consideration for my friend, Mitsumura. It might sound conceited of me, but I thought I was being pretty nice. But for some reason, Mitsumura looked at me in dismay.

“Hey, Kuzushiro, are you familiar with an old saying about counting chickens before they hatch?”

“Of course I am.”

“Well then you must not be remembering it right. It means you should worry about what to do with that solution once you have it.”

Mitsumura gave a deep sigh.

“Here you were acting all cool and mysterious, but you were actually thinking something stupid. I am shocked and appalled. If you're able to solve the locked room mystery, why don't you go ahead and announce it to the whole world? Well, that day will never come, not in a billion years.”

This was getting on my nerves. I glared back at her.

“Don't say things you'll regret.”

“There's no way I will. If there's no risk, then there's no enjoyment, either. Ah, that's right, do you want me to help you a little?”

I was taken aback by the offer and immediately responded.

“I don't need any hints. I'll figure this out on my own.”

“It's not a hint,” Mitsumura said with a shrug.

“Not to the locked room, at least. I'm offering to tell you who the culprit is.”

“Huh?”

The unexpected words froze my brain for a moment. I stammered out a response.

“Do you already know who the culprit is?”

“Of course.” Mitsumura puffed out her chest. “Who do you think I am?”

“I think you're a light speed detective clown.”

“You think of me like that?”

Mitsumura looked to enter a state of shock. Then she cleared her throat.

“Anyway, I'll tell you who the culprit is. You want to hear it, right? Well then I'll tell you.”

“Wait a minute!”

I hurriedly stopped her. The identity of the culprit was certainly a concern. But was it okay for me to ask Mitsumura for that? After all, we'd had a falling out and become enemies.

When I told Mitsumura about my concerns, she let out an exasperated sigh.

“What are you talking about? You should just be quiet and listen,” she said as if it were obvious. “Who the culprit is is way less important than the solution to the locked room, right? That's why I'm going to tell you their identity. If you really want to solve the locked room mystery, you have to focus entirely on the locked room. You don't have time to worry about other things. Give yourself entirely over to the locked room. Otherwise, you'll never be able to solve it.”

She aggressively forced all that on me. I gradually began to come over to her side, and in the end, I obediently asked her who the culprit was.

“Then I'll tell you.”

Mitsumura cleared her throat.

“The one who committed the crime is...”

When I heard the name, my eyes widened. I see... so that person is the culprit. That's a surprise.

“...By the way, I'm sure you have a reason for saying that?”

“Of course. Why are they the culprit? Because...”

Blah blah blah, she explained her reasoning. I see... so that's why they're the culprit? It made sense.

“Now do your best. Not that I think you'll ever solve it,” Mitsumura said, forcibly ending our conversation. Just before closing the door, she pulled something out of her pocket and handed it to me, saying “Oh, right, take this with you.”

“I'll let you have it, Kuzushiro.”

It was a playing card with the eight of hearts on one side. The only playing card that hadn't been used in this incident, taken from Riria's smartphone compartment. The corresponding rule from Knox's Ten Commandments was...

The case can't be solved with any clues not presented to the reader.

I stood staring at the card I'd been given for a while. Did that mean that all the clues to break the locked room had already been revealed?

I returned to the library and shook the jam jar containing the master key. It was a jam jar with a diameter of about 20 cm and a height also of 20 cm. It didn't have a label, so I didn't know if it was actually a jam jar or not. But it looked like a jam jar you'd see in a supermarket, except that it was larger. Maybe it was for business use.

I thought as I shook the jam jar. If the culprit had used the master key to lock the door, there would be three major obstacles in their way. Those were ① How did they get the key inside the room? ② How did they get the key inside the jam jar and close the lid? And ③ How did they recover or destroy the device that closed the lid?

“.....”

No, it was impossible. I put the jam jar down on the floor. Even ① by itself would have been impossible, but it continued on to hit us with ② and ③ It was a triply impossible crime. Did the culprit... not use the master key to lock the door?

Three years ago, in the incident Mitsumura was said to have caused, the room key hadn't been in a jam jar, but in a desk drawer. Did that mean the same trick could be used to put the key in a jam jar or a drawer? Or did the fact that the keys were found in two separate locations mean that they weren't used at all?

There were other things I was concerned about. One was why the culprit moved the body. The culprit moved Yashiro's corpse from his room in the west building to the library. I didn't think they would have done that for no reason, so it must have benefited them in some way.

Another thing that bothered me was the mystery of the vanishing tape. When Mitsumura had seen the piece of cellophane tape removed from the library door, she'd realized the truth behind the locked room. That cellophane tape had been used to attach the gachapon capsule lid. It was probably the culprit who'd collected the piece of tape, and the question remained: why did they do so? And even more questionably...

In the incident three years ago, there wasn't any gachapon capsule on the door.

In that case, the piece of tape retrieved by the culprit may have had another meaning. In other words, it was possible the culprit hadn't needed the tape to stick the capsule to the door, but used it for another trick and stuck the capsule to the door to camouflage the traces. So, unlike three years ago, in this case, there were some circumstances that prevented the culprit from just retrieving the tape from the door at the time of the crime.

“Hi, Kuzushiro! How's it going?”

Yozuki chose that moment to interrupt. Like a flock of scared pigeons, my thoughts all flew the coop. Man, and I'm pretty sure I was on to something, too.

I glared at Yozuki in frustration. Yozuki glared back at me.

“So? Make any progress?”

After about a minute of us staring each other down like a pair of delinquents, Yozuki returned to the topic at hand. I sighed once, pouted, and said “It's as you can imagine.”

“This whole case is a labyrinth.”

“You can't give up this early!”

“Well I don't know what else to do.” I'd been sitting there thinking for about two hours now, but I was no closer to an answer. “The strength of the locked room is too high.”

“The strength of the locked room.?”

Yozuki tilted her head. Just for a change of pace, I explained.

“Put it simply, it's like a difficulty level for locked rooms. For example, in this locked room, there's no gap under the door, right? In that case, we can't use any trick that uses a gap under the door, so the range of potential tricks becomes narrower. It's like an added restriction.”

Hearing my explanation, Yozuki furrowed her eyebrows.

“I don't really get what you're talking about.”

“You don't?”

That was disappointing. Yozuki shrugged at me.

“Well, you keep thinking about it – there's still time. I have a busy schedule of relaxing in the lobby drinking tea ahead of me.”

“How enviable.”

“Maybe I'll try the strawberry shortcake, too.”

“Seriously?”

After Yozuki left, I collapsed to the floor. I stared at the ceiling as I thought. As she'd said, there was still time. Today was the fifth day since we were trapped in this closed circle. Assuming rescue would come in a week, we had three days left, counting today. In three days, the case would be turned over to the police and taken out of my hands. If that happened, I wouldn't be able to examine the locked room this closely anymore.

Three days... But I felt like I could manage to solve everything in three days.

If only I got them...

...Absolutely nothing happened, and I remained trapped deep in the labyrinth. Every day, I wracked my brain at the crime scene, but I couldn't form even the beginnings of a solution, let alone expose the trick. I was on the verge of death, both mentally and physically. Mitsumura snorted and laughed at me every time we passed each other in the hall. It seemed her pride had worn me down.

It had been seven days since I'd come to this mansion. Rescue would probably be coming today or tomorrow. Perhaps because of that, everyone gathered in the dining hall that morning had bright, cheerful faces. The fact that no one had died since the fifth day when Yashiro was killed was also likely a factor.

I sat across from Yozuki, rubbing my eyes after pulling an all nighter. She was spreading jam on toast. The toast had been made by Miss Meirozaka. There were also fried eggs, salad, and sausages spread out on the table. Those were also made by Miss Meirozaka. Although it wasn't as good as Ms. Shihai's food, it was still above the threshold of “delicious”.

I spread some marmalade on my toast as I held back a yawn. Then I spread some apple jam. It was a hybrid of apple jam and marmalade. I placed my toast on the plate and put the lids back on the marmalade and apple jam. Yozuki, who was watching me, chided me.

“Kasumi, you mixed up the lids.”

“Mixed up the lids?”

“Yeah, you see? The jam jars are...”

Yozuki picked up the jars of marmalade and apple jam in her hands, she unscrewed the lids and replaced them on their correct jars. Each lid had a picture of an orange and an apple on it. Apparently, I'd mistakenly put the lids on the wrong jars. And Yozuki had chided me for...

I figured it out.

I shot up from the table. I dashed straight for the library. “Huh? Kasumi, what's wrong?” I heard Yozuki's panicked voice behind me. But I didn't care. I ran through the lobby to the west building. When I arrived at the third floor library, I stopped to catch my breath.

I looked around the room. And I let out a breathy half-laugh of admiration.

Ah... I hadn't noticed it. There were probably only three people in the world who would think of something like this. Me, the culprit of this case, and Shitsuri Mitsumura.

“Kasumi, what's going on?”

Yozuki had chanced me. As she caught her breath, I told her.

“Yozuki, please gather everyone in the dining hall.”

Yozuki tilted her head.

“Everyone's already gathered there. We were eating breakfast.”

Was that so? Come to think of it, that was right. I coughed.

“Kasumi, what's wrong?” Yozuki looked at me suspiciously. “Are you still half asleep?”

I shook my head. I wasn't half asleep. Even if I had been, I'd completely woken up.

“I've solved it.”

This ending had completely opened my eyes.

“I've solved the locked room mystery.”

 

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