"But who are you?"
Hattori Heiji took off his hat and introduced himself after hearing my words.
"My name is Hattori Heiji. Like Shinichi, I'm a high school detective. Nice to meet you."
Hearing that, Kogoro spoke as if he remembered something.
"Now that you mention it, I've heard there's an excellent high school detective in the western region."
"Yes, they always compare us: Heiji in the west, Shinichi in the east. So I came to check."
Ran, hearing this, asked Heiji.
"Check what?"
"Whether Shinichi really has the qualifications to rival me or not!"
"You might have come to the wrong place? I haven't seen Shinichi in a while either."
"Really? Hmm... Well, since I heard Cassian is your fiancé, maybe you wouldn't know."
At those words, Ran blushed and didn't know what to do.
"Hey, fiancé..."
Then Conan flared up and asked.
"Who said anything about a fiancé!?"
"A girl named Sonoko said so, but why are you getting angry?"
"Ahaha... Since she's a close older sister, I was curious..."
At that moment, a knocking sound came from the entrance. As we turned, a woman had already entered and was standing there, frowning and tapping on the door frame.
Knock knock knock!
"How many times do I have to ring the doorbell? This office's customer service is a mess."
Kogoro looked at the woman and spoke.
"W-what can I do for you?"
First, Kogoro guided the woman to the guest table and sat her down to talk. Ran prepared tea and gave it to the woman and Kogoro.
"So you want an investigation into your son's girlfriend?"
"Yes. Here are photos and her background information."
The woman handed several photos and documents to Kogoro.
"Yukiko Katsuragi, 24 years old. Graduated top of her class from Mitsuba High School... Currently enrolled at Toto Medical University. Working diligently to become a doctor..."
Kogoro, puzzled, asked the woman. Because the documents she handed over showed no particular issues. On the contrary, she had good specs and was a diligent woman.
"Um... Do you have any complaints?"
"No. There's nothing like a complaint. Just..."
Cutting off the woman's words, Heiji spoke.
"She's too perfect, so you don't like it, right?"
"What?"
"Humans are all suspicious and jealous animals. When they see something perfect, they try to find flaws. Right?"
The woman looked at Heiji and spoke.
"Who is this?"
"Ahaha, he's my daughter's friend."
Kogoro gestured to Heiji not to interfere.
"Anyway, let's discuss the details at my house. My husband is waiting too..."
"Huh? Go now? Then why didn't both of you come together from the start..."
"As I mentioned earlier, he's a diplomat, so if it gets known that he frequents such places..."
Heiji cut in again and spoke.
"He'll become the subject of gossip. That's what you mean, right? Alright, I'll go too!"
"What!?"
"Taking kids along will raise less suspicion than you going alone, mister."
Hearing that, the woman agreed.
"I see. Then, please."
Following Heiji's words, we decided to go along. Since Conan said he'd come too, I spoke.
"Conan, it might be better for you to rest at home? You have a cold."
"I got a shot, so I think I'm getting better."
I touched Conan's forehead and checked his temperature.
"Hmm... I don't think so? Do you really want to go?"
"Yes."
"Then there's no choice."
I put earplugs and a mask on Conan, wrapped him tightly with thick cloth like a swaddle, fixed him on my shoulder, and moved.
"Bro, you don't have to do this..."
"Ah~! Cold wind is bad for a cold."
Ran saw that and laughed as she spoke.
"You look just like a dad carrying a baby."
At those words, I showed Conan to Ran and said.
"Our baby Conan. Cute, right?"
"Huhuhu~ Yes, very cute."
"Ugh! Put me down now!"
"No."
Ran burst out laughing at that sight.
"Pffft~"
So we moved to the diplomat's house. As if it became fun, Ran now teased Conan more. In the middle, Conan couldn't take it and threw a fit while being carried, but the cloth tied tightly with a ship's knot using strength beyond human didn't come loose.
"Ugh... Damn it! Such humiliation..."
"Oh my, the child is full of energy."
"Right? I'm thinking of making him an athlete later."
Hahaha~ Hohoho~
Then Kogoro spoke.
"We seem to have arrived now, so we should be quiet."
"Yes."
We entered the diplomat's house. It was quite a large house. Similar in size to my house.
"Now, please come inside."
"Ah, yes."
Inside, a butler greeted us with a bow.
"Welcome back, ma'am?"
"Where is he?"
"He's probably still in the study on the second floor. But who are these people?"
"This is Mr. Mouri, an old friend."
"I see. Shall I bring something?"
"Yes."
At that moment, Yukiko, the real person from the photos shown by the woman, came and greeted the woman.
"Mother! I came to visit."
"How did you get here?"
The son of the house, who was behind, spoke.
"I called her. Since father wouldn't meet Yukiko, I had no choice but to ask her to come. But father hasn't even come out of the study."
Yukiko looked at us and spoke.
"Oh, are you mother's friends? Huh? Is that the onmyoji Cassian???"
"Nice to meet you. I'm Cassian."
"Wow~ Meeting a celebrity... But who is the child you're carrying?"
"Ah~ This child is a younger acquaintance who has a cold."
"I see."
Then the woman frowned and spoke.
"Don't be presumptuous. And why are you calling me mother!? You don't know your place!"
"I'm sorry..."
The woman scolded Yukiko and then guided us again.
"Now, let's go this way."
"Ah, yes, yes."
As we followed the woman's guidance to go up to the second floor, an old man was coming down the stairs in front of us.
"Oh, father, when did you come?"
"What are you talking about, dear? You called me because you wanted to hear about the fish I caught, right?"
The grandfather showed a fish print he made by stamping a fish he caught on paper, boasting.
"How is it? Quite a big one, right?"
"Ah, yes... Really. Then please go to the living room first. I'll be right there."
"Okay."
Kogoro glanced at the old man going down the stairs and, puzzled that the woman made such an appointment despite the investigation taking time, asked.
"Is it okay to make such an appointment?"
"It doesn't matter. He'll forget soon anyway. Father's memory has been getting worse lately."
"I, I see."
We arrived in front of the study door on the second floor, and the woman knocked on the study door.
Knock knock knock!
"Dear, we have guests! Dear?"
There was no response from inside the study.
"Strange... Is he not inside?"
The woman took a key to the study from her handbag and opened the door. Inside, a man who appeared to be the diplomat seemed to be sleeping with his chin on the desk, and music was playing in the study.
"Oh my. Leaving the audio on and sleeping in a place like this... Dear, wake up! Dear!"
The woman tried to shake the diplomat awake, but the diplomat fell to the floor as he was.
Thud!
"Ah!! Dear!! Wake up!"
I, Kogoro, and Heiji hurriedly approached the fallen diplomat to check his condition.
"Oh no, he's already dead."
"Ah... That can't be..."
The people from the lower floor heard the noise from upstairs and hurriedly came up.
"Ma'am, what happened?" "Father?"
Seeing that, Kogoro spoke.
"Stay there!! Don't enter this study until the police arrive! Ma'am, don't move from there either!"
"What happened?"
"The owner of this house, the diplomat, has passed away."
"What!!!???"
Conan, being carried by me, tried to see the situation by sticking his face over my shoulder. So I slightly bent down to show him the situation.
"Goodness, more detective play? Here! Look here~"
"Ahaha thanks, bro."
I pretended to look at the corpse. Since I already knew the original story and who the culprit was, but couldn't say it outright, I had to at least pretend to look at the evidence.
"Still warm? And the lips and fingertips are starting to turn purple. That means he hasn't been dead long, and it's poisoning."
"Bro! Over there."
Looking where Conan pointed, I saw something like a puncture mark near the diplomat's neck. I immediately called Kogoro.
"Detective!"
"What is it? Son-in-law."
"Take a look here."
I explained what Conan and I found to Kogoro.
"I see. He really hasn't been dead long. Plus, the lips are starting to turn purple and there's a puncture mark, so this is poisoning. Then there must be a poison needle too."
At that moment, Heiji pointed to the floor where the poison needle was and spoke.
"Here it is. I just found it."
"Good, don't touch it as there might be fingerprints."
"Understood."
Heiji, seeing that Kogoro wasn't good at deduction, took the lead to speak, but since I had explained to Kogoro this time, Heiji didn't step forward to do or say anything.
"Conan, how's the cold?"
"I think it's much better since I got the shot."
"Still, when you get home today, take medicine and rest well."
"Okay, thanks."
Since he didn't drink the pepper drink, Conan's condition didn't look bad. After a short wait, the police arrived. Naturally, Inspector Megure came again. The forensics team entered and began examining everywhere.
"Hmm... All the windows are locked from inside. It would be difficult to enter from outside. Then we have no choice but to think that someone among you used the key to enter through the only entrance."
Inspector Megure looked at the woman and asked.
"Ma'am. How many spare keys are there to this study?"
"There are only two keys. One is this key I have, and the other is with my husband."
"With your husband?"
"Yes, he always carries it in his pants pocket."
Inspector Megure rummaged through the dead diplomat's pants. Then, a key was folded and inside the coin pocket of the pants pocket.
"This can't be..."
At that moment, I spoke.
"A locked-room murder."
"Right."
Conan also nodded, agreeing with those words. The reason it's a locked-room murder is that the study door was locked when we arrived. But one of the two keys was with the woman who came with us, and the other was with the diplomat, so simply put, it was impossible to commit the crime, lock the door, and leave.
"Son-in-law, why is it a locked-room murder?"
I explained to Kogoro.
"Ah~ I see."
I quietly spoke to Conan.
"Conan, I know who the culprit is. Have you figured it out?"
"What? Really?"
"Yes. Should I tell you?"
Conan thought for a moment and refused.
"No, I'll try to deduce it myself."
"Oh~ Let's see the skills of the boy detective team?"
"But help me a bit. Since you're an adult, you can easily move around here and there."
"Okay."
At that moment, the forensics team found something strange about the key and reported it.
"Inspector! The key the victim had is a bit strange!"
"What!?"
We went to check the key. The key had a flat, egg-shaped keyring attached, and the flat part was made to split in two.
"Ah! Isn't this Scotch tape?"
Between the split keyring, there was Scotch tape attached, and as if something like thread was stuck, a thin line was raised in the center of the tape, leaving a mark.
"Oho~ This is getting interesting."
"Bro, let's go check other rooms first."
"Okay."
Conan and I went to various rooms, collected evidence, and returned. Then Heiji appeared triumphantly and spoke.
"I've figured it out! The locked-room trick and who the culprit is."
"What? You've already solved it?"
"Yes, it looks like a perfect locked room, but there's one gap."
"Gap?"
"There's a gap under the door, right!"
"Hahaha, you're not going to say it was thrown through the door gap, are you? That's impossible."
"It's possible. With Scotch tape and this fishing line with a needle I just found."
Heiji went to Inspector Megure and asked for a moment of help.
"First, please play the role of the corpse."
"Ah, sure."
Heiji attached the fishing line to the keyring using Scotch tape, threaded the fishing line through the pocket using the needle, connected it to Inspector Megure's pocket, and then, holding the fishing line and key, slowly went outside, locked the door with the key, and pulled the connected fishing line, demonstrating how the key automatically passed through the gap under the door and into the corpse's pocket.
"Oh! It really went in."
"And finally, by pulling hard, the fishing line comes off the tape, and no evidence is left."
"That's true. Then who is the culprit?"
"Considering the time to harm the victim and complete this trick, and the time of the crime, the only culprit is the grandfather."
"What!?"
"The fishing line with a needle I found in the living room is the evidence! This fishing line is made from a new material, a special thin and tough fishing line. Since you enjoy fishing, you won't say you don't know it, right? Moreover, when the woman and we were on our way to this study, the woman said this, right? 'Then please go to the living room first.' In other words, after committing the crime, you went to the living room, confident it was a perfect crime, and threw the fishing line in the living room trash can. That's the decisive evidence."
The grandfather was sweating cold sweat.
"How about it. Isn't that right!?"
"Huhu, I really can't do bad things. Yes. It's me."
At that moment, I spoke.
"That's not it."
"Cassian!"
"The trick Heiji just mentioned is impossible."
"What???"