I examined the corpse and determined that the time of death was between nine to ten hours ago, which was consistent with the bartender’s statement.

I detected the smell of cigarettes and alcohol on the victim’s body. I then used Organ Echolocation and found that all her internal organs were in normal condition except her lungs, which were especially hardened.

I noticed yellow burnt marks on the victim’s fingers and remarked, “The victim had a habit of smoking cigarettes. Her lung fibers are practically rock hard!”

“Yes,” Xiaotao nodded. “According to her friends, she’s a chain smoker and she usually smoked about thirty cigarettes a day.”

“Wow!” cried Bingxin. “Your ears are even more sensitive than X-rays, Song Yang-gege!”

I briefly explained the principles of Organ Echolocation to her and she was both fascinated and impressed by it.

There were stains on the victim’s chin and chest. When I pried open her mouth, I detected the smell of alcohol. The back of her teeth seemed to be corroded by stomach acid, which meant that she probably vomited not long before her death. It wasn’t clear if that was caused by some kind of poison or if it was just because she was drunk.

The victim’s vomit would be an important piece of evidence. I asked Xiaotao about it and she said, “It’s been collected and the forensics team is testing it right now. So far nothing significant has been found.”

“Impressive!” exclaimed Bingxin. “You even thought of such details…”

“Am I the only one who found it disgusting?” Dali interjected.

We glared at him in unison, and Dali bowed his head with great shame.

In addition to the smell of alcohol, I detected some other smells too. I sniffed at the victim’s mouth and nose and collected her nasal residues with some cotton swabs. I gave them to Dali and asked him to take it to Xiaozhou for testing. I suspected that chloroform would be found.

As he was about to leave, I thought of another thing and stopped him. I pulled a bottle of chemicals from my bag and asked Dali to freeze the contents in the bottle into small ice cubes. I would be using it later.

Bingxin and I put on latex gloves and we began to cut away the victim’s clothes with scissors. I examined her whole body over and over again and finally found a needle puncture wound on her waist. Judging from the sign of bleeding, it should’ve occurred before the victim’s death.

I suspected the puncture wound was left by the murderer as the poison was injected into the victim’s body, but it was too soon to tell. There was nothing left to do so I took off the gloves and waited.

“Was the victim one of Cheng Yahui’s patients?” I asked Xiaotao.

She nodded.

“We found her medical record at her house. She went to see Cheng Yahui three months ago.”

Bingxin’s eyes widened.

“This proves that the guy’s definitely the murderer!” she exclaimed. “But how did he kill the victim last night? Weren’t the police monitoring him?”

“We were,” replied Xiaotao. “According to the officers who shadowed him, he went to the same bar that the victim was found last night. This man is getting more and more suspicious. I’ve asked Yuanchao to bring him back to the station. Once you’re done with the autopsy, we can go meet him in the interrogation room straight away!”

“Can I go too?” Bingxin asked eagerly.

“Sure,” said Xiaotao. “But the names of the interrogators must be recorded and then the document would have to be signed by Sun Tiger later. Are you sure you want to come?”

“Never mind…” replied Bingxin, all deflated.

At that moment, Dali burst into the room and shouted, “Dude, they really did find chloroform in the victim’s nasal residue!”

“What about the ice cubes?” I asked.

He handed me an ice tray and said, “Here you go. They’re not completely frozen yet, though.”

“It’s good enough!”

I put the gloves back on and picked out one of the ice cubes. I rubbed in around the puncture wound and the blood vessels under the skin began to appear. In addition to the red blood vessels, there were purple veins too.

“Wow!” Bingxin cried in surprise. “What did you use to make the blood vessels appear?”

“A chemical that contains ephedrine,” I answered.

Bingxin thought for a while and commented, “That is clever, Song Yang-gege! Ephedrine constricts blood vessels and makes them more prominent. But why didn’t you just use alcohol?”

“Alcohol can only constrict the blood vessels when its rapid evaporation cools the skin. How would it work on the cold skin of a corpse?”

“I didn’t think of that!” exclaimed Bingxin after sticking out her tongue.

I traced the ice cube along the purple vein. This was the path that the poison took to spread through the body. It ended on the chest and spread in a wider area there.

“The poison entered the victim’s lungs,” I stated. “Looks like the hardness of the lungs was due to lung failure, not excessive smoking. But what poison can cause this effect? Cyanide? Hydrocyanic acid? No, the symptoms don’t match up… Carbon monoxide? No, that’s a gas… Ricin? No…”

Bingxin used a cotton swab to collect some blood from the puncture wound, then she said, “I’ll do some testing on it in the lab next door. Let’s see who finds out the answer first, Song Yang-gege!”

“Deal!” I said. “Whoever loses has to treat the winner to a meal!”

Bingxin laughed. “Then get ready to take me out for dinner, because I’ll definitely beat you to it!”

She then took her box and ran out.

“Do your best, Song Yang!” Xiaotao laughed. “Don’t lose to Miss Sun!”

“I’m actually not that confident this time…” I smiled wryly.

Drug tests were my kryptonite, and right now, I just couldn’t think of any poison that would match the victim’s symptom. Still, I wouldn’t just give up on myself. I examined the victim’s body again, this time more thoroughly. I checked the victim’s vagina too, which prompted Dali to ask, “Why do you always check that part of the body, dude? It’s almost like you enjoy it.”

“Shut up!” I snapped. “Some poisons are diuretic, which means I have to check the victim’s residual urine.”

However, this poison didn’t seem to have a diuretic effect at all. Not only that, but there were just no other signs throughout the body at all. This made me worry. I no longer cared about winning the bet with Bingxin. I just hoped that she could figure out the answer as soon as possible.

Suddenly, Bingxin burst through the door with plastic goggles resting on her head. She smelled of some chemicals.

“I’ve figured it out, Song Yang-gege!” she shouted.

“Oh my god!” cried Dali. “You actually lost to her, dude!”

“My specialty is in autopsy,” I said. “I’m not good at drug testing at all. Tell me the answer, Bingxin!”

“Why don’t you guess what it is? The name starts with an ‘N.’”

“We’ll be here all day if you wait for me to guess the right answer.”

“Come on, Song Yang-gege!” she insisted. “You must know. It’s Dad and Uncle Wang’s favorite poison!”

I suddenly had an epiphany.

“Nicotine!” I cried.

“Correct!” Bingxin exclaimed while clapping her hands. “It’s nicotine at a concentration that’s high enough to kill!”

“Clever!” I remarked. “Very clever!”

Bingxin blushed.

“You’re too kind, Song Yang-gege!” she mumbled. “If you hadn’t said that the poison spread in the lungs, I wouldn’t have thought of it myself…”

“No, I don’t mean you,” I replied. “I was talking about the killer.”

Bingxin’s expressions turned sullen immediately. Xiaotao covered her mouth and tried to hold in laughter. Only then did I realize that I’d spoken without thinking again.

Fortunately, Bingxin was a cheerful girl. Her expressions soon returned to normal.

“Why did you say the killer is clever, Song Yang-gege?”

“Well, think about it,” I said. “The businesswoman had a stomach problem, so the killer poisoned her medicine. The student loved to beautify herself, so the killer tampered with the Botox. The model was promiscuous, so the killer poisoned the condom. And now, the fourth victim was a chain smoker, so the killer poisoned her with nicotine! The killer obviously has a meticulous and cunning mind!”

“My lecturer once said that anything can be poisonous,” said Bingxin. “The only thing that differentiates something from being toxic and non-toxic is the dosage. Even salt and sugar can kill us if consumed excessively. I think the killer must have deep knowledge in pharmacology and toxicology. With slight adjustments in the dosage, the killer turned Botox and nicotine into murder weapons!”

I glanced at the victim. If it wasn’t for the puncture wound on her waist, her cause of death might’ve never been found. After all, further testing would only show that there were high levels of nicotine in her lungs, which checked out with her history of being a chain smoker.

I couldn’t help but feel for the murderer. These murders were so close to being perfect crimes!