"After administering both a 5% sodium bicarbonate solution and a 20% mannitol solution to the patient as you requested," reported Gregory, Kaede Hoshino, and Chiba as they returned to Hiroji Nagano's HCU ward. "The patient's vital signs have stabilized, and the brain waves have become active again."

"Very well," said Grigory, sitting in a chair in the room. "Then we can wait for the sleeping prince to wake up."

At that moment, something suddenly sounded on Gregory's body - it was a BP machine.

"......" Grigory glanced at the numbers, and then a look of surprise flashed across his face. Three young men and five small children were coming to visit the patient. ”

“？” Thousand Feathers raised an eyebrow.

Five little kids...... Why does he always think that it might be someone he knows...... If there was one thing that called the little ones and Gray Plains after Conan disappeared, it was exactly five people.

……

Chiba stood in the staircase, looking at her phone. Just then, Conan walked in from downstairs.

"Where did you go before?" Qian Yu asked. "You added that toxicology test, right? Did you go to the scene? ”

"Investigate the case," Conan explained with a smile. "I understand who is responsible for his condition."

"Who the hell?" Qian Yu frowned, and then fell into deep thought. "Speaking of which, Mr. Gregory had already tested the poison gas methyl bromide at Mr. Hiroharu Nagano's house, and then he said that he had understood, and he had not checked what the poison gas was......

"Mr. Grigory is a doctor, and even if he will investigate how the methyl bromide comes from, it does not mean that he will investigate the deeper causes." Conan spreads his hands. "And I'm here to find a deeper reason - and it's related to one of his three apprentices!"

"Huh?" Qian Yu was stunned.

At this moment, something rang out in both Chiba and Conan's pockets at the same time - it was the communication badge that Koji Nagano had given them earlier.

As they pressed the communication button, Gregory's voice rang out. "Aren't you two going to come? Especially the bespectacled imps - I want to see what the little ones say you can give a surprise; And I'd like to talk to you about the forgery order as well. ”

The corners of Conan's mouth twitched. "Uh...... Okay, I'll be over soon. ”

Hanging up the badge, Chiba and Conan walked out through the door next to Chiba together.

……

By the time they returned to HCU, Hiroshi Nagano had woken up and seemed to be in good spirits. Gray Yuan and the others, the three apprentices of Hiroharu Nagano, Lady Nagano and Gregory and their team had all gathered in this large ward—it would not have been possible to accommodate them in a regular ward, but this HCU was quite spacious, and even if it had accommodated all of them, it still didn't seem too crowded.

"You're here too," Gregory glanced at Chiba and Conan as they walked in. "Alright then, Mr. Nagano, we've investigated the cause of your illness."

"Because of what?" Mrs. Nagano asked.

"Lady Nagano," Gregory asked. "When did you buy this house?"

"Hmm," Mrs. Nagano thought for a moment. "About twenty years ago."

"Second-hand housing?" Grigory continued.

"Yes." Mrs. Nagano nodded.

"Sure enough," Grigory nodded. "Then everything makes sense."

"What do you mean by that?" Lady Nagano wondered.

"Your house is not an only child," Gregory said, turning his cane around. "A few decades ago, it was likely that this house shared the same central air-conditioning system as the house next door through a pipe buried in the ground. I don't know why, maybe the person who sold the house to you is the owner of the house next door? ”

"However, the workers who were fumigating next door couldn't have known about it, so they performed the methyl bromide fumigation directly in that house, and the methyl bromide went straight into your abandoned but unsealed central air conditioning duct along with the air conditioning duct and eventually leaked out."

"Then why am I okay?" Mrs. Nagano asked. "If that's the case, I should have been poisoned too?"

"You are indeed poisoned, too," Grigory shrugged. "Your previous blood sample was tested for methyl bromide, and the results showed that you had a certain amount of methyl bromide in your body, but because the amount was not very large, you did not have serious symptoms. As for why you don't have a lot of it in your body..."

"The molecular formula of methyl bromide is CH3Br, and the density of air is about the same as a gas with a molar mass of 29 (between ethane and ethylene), which means that methyl bromide is heavier than the mass of air, so after leaking out of the central air conditioning duct, there will be more methyl bromide trapped on the ground floor of the house - although Mrs. Nagano has a single bed in your room, Mr. Hiroji Nagano is used to sleeping on the ground, so he inhales much more methyl bromide than you do when he sleeps. Therefore, by the time Mr. Hiroji Nagano reaches the threshold for the onset of the disease, the level of methyl bromide in your body will not be a big problem. ”

At that moment, Conan suddenly spoke.

"Or there's another possibility, someone plugged the baffle into the central air-conditioning system ducts while others weren't looking, and drained all the methyl bromide into Mr. Nagano's room."

"Am I right? The owner of the house next door, the son of the former owner of the Nagano house. Conan turned his gaze to one of the three apprentices - if Chiba remembered correctly, he was the one who speculated that he might be looking at Tang Sancai before he found out that Hiroshi Nagano was unconscious...

"What do you mean by that?" The apprentice who was being watched by everyone looked at Conan with some annoyance.

"Just twenty minutes ago, the Metropolitan Police Department's biochemical personnel raided the house next door in your name - rest assured, they got permission from their superiors." Conan said. "Then I found a small working fan in the pipe that connected your house to the Nagano house - this fan was constantly blowing methyl bromide towards the Nagano house."

"And just a minute ago, they entered the Nagano house for a raid and found a plastic baffle with your fingerprint on it in the pipes of the central air conditioner, and this baffle stopped most of the incoming methyl bromide into Mr. Nagano's room."

"Now, would you like to speak to everyone here?" Conan leaned against the glass wall. "I'm sure you have some reason for doing this, right? Let's hear it for everyone.