We went outside and saw Cheng Yahui lying on the ground. He was crouched in a fetal position and was still conscious, but he was writhing and groaning in pain.

Xiaotao kicked him and said, “Get up! You’re trying to frame the police, aren’t you?”

“Wait,” I stopped her. “It looks like he’s been poisoned!”

I pulled up his eyelids and checked his pupils. They were contracted, and his eyes were bloodshot—these were clear signs of poisoning. But who could poison him? He’d been in police custody since morning!

I told Dali to quickly get some soapy water to induce Cheng Yahui to vomit. Suddenly, Cheng Yahui clutched at my wrist and with much effort told me, “My medicine… I left it in the interrogation room…”

Xiaotao ordered an officer to check the interrogation room immediately. He then returned a few minutes later with a bottle of medicine under the desk. It was labelled as tranquilizer. No one dared to give Cheng Yahui the medicine. What if it ended up causing his death? That would cause the police immense trouble. The safest thing to do right now was to induce vomiting.

But when Cheng Yahui saw the medicine, he almost frantically pleaded, “Give it to me… I’ll be in terrible pain if I don’t take it…”

“No,” Xiaotao refused. “We need to test it first.”

“No!” he yelled. His face was distorted by pain. “Give me! Now!”

I had a sudden epiphany of what was going on and grabbed the medicine from Xiaotao’s hand and stuffed it into his mouth.

“What are you doing, Song Yang?” Xiaotao was in utter shock.

“Don’t worry, this is the antidote!”

Less than a minute later, Cheng Yahui recovered.

“Terribly sorry for that,” he said. “I have neuralgia. If I don’t take this medicine every once in a while, the symptoms will appear.”

“Who prescribed this medicine for you?” I asked.

“I do it myself, of course,” he replied. “I’m a doctor after all.”

“But you’re a gynecologist,” I argued. “How would you know how to treat neuralgia?”

“Please!” Cheng Yahui laughed. “I’m a certified medical doctor! Why wouldn’t I understand such a simple disease?”

“Nevertheless,” I frowned, “could you please sit down and wait for a while? We’d have to do some testing.”

Cheng Yahui was hesitant, but there was nothing he could do. We asked for his urine samples and Bingxin tested both his urine and the medicine. After half an hour, Bingxin came out of the lab and announced, “I couldn’t identify the ingredients in the medicine, but I found traces of atropine poison in his urine sample.”

“It’s Yin and Yang poisoning!” I cried.

“What?” asked Xiaotao in confusion.

“It’s a poisoning technique that my ancestor recorded,” I explained. “You’d put two substances in two different food dishes. If someone ate only one of those, they’d be fine. It’s only when both are eaten that the poison would take effect. You can also do the opposite—by adding poison to one dish and the antidote in another. You could poison your guests by eating the same dishes with them and then save yourself by taking the antidote later.”

“That’s just like the synergistic and antagonistic effect that we learn in our toxicology class,” Bingxin remarked. “Sometimes two drugs can become poisonous when ingested together, or they can inhibit the other’s effects, meaning one drug might turn the other drug into a harmless substance.”

“We would’ve never figured this out if Cheng Yahui hadn’t collapsed here,” I said. “The murderer must’ve done this to Cheng Yahui, which means that the murderer is likely someone close to him!”

When I put it that way, everyone had the same person in mind—Qu Tingting!

We brought Cheng Yahui back into the interrogation room. He insisted again and again that he prescribed the medicine himself. Then I asked him, “Who gets the medicine for you?”

“Nurse Qu,” he answered.

“What is Nurse Qu’s educational background?” I asked.

“I don’t know,” he said. “Some nursing college, perhaps. I don’t talk to her much.”

Xiaotao waved her hand to let him leave. Everyone fell silent once he was gone. All of us had overlooked this blind spot. Qu Tingting was clearly the real culprit! Her motive was most likely jealousy.

“What are we waiting for?” Xiaotao suddenly shouted. “Let’s go catch the murderer!”

We hurried to the university hospital, but Qu Tingting was already gone. All we could do was to ask the head nurse to call her.

“Damn it!” cursed Xiaotao with frustration. “She must’ve run away when she saw Cheng Yahui getting arrested! She must’ve known that her whole plot would be exposed once Cheng Yahui was questioned.”

“Let’s go to the gynecology department,” I suggested.

We went into Cheng Yahui’s office. It was all neat and tidy except for a stack of papers on the desk. Xiaotao rummaged through the whole room and sighed, “There’s nothing here.”

“Wait!” I went to the desk, took a pencil, and smeared the whole piece of paper until a few lines of words gradually appeared.

“Dr. Cheng,” it said, “I must leave now. I will be gone for quite a long time. I prepared the medicine for you. Please remember to take it. It won’t be enough for long. When you run out, I will tell you the formula for the antidote if you come and see me. Also, I have something important to tell you…”

The words stopped after that. It seemed that Qu Tingting hesitated and tore off the paper at that point.

“She will be gone for quite a long time…” remarked Xiaotao. “Is she going to turn herself in?”

I thought for a while and suddenly realized something.

“There’s no difference in the punishment received for killing four people as opposed to five people, is there?” I asked.

“No,” answered Xiaotao in shock. “You’d be sentenced to death in both cases. Wait, are you suggesting that she’s going to kill that florist?”

“It’s very likely,” I said. “Let’s go find her now! Maybe we can still save her life!”

Xiaotao called the officers who were still at the station and asked for the florist’s address. We immediately rushed there and was greeted by a beautiful young woman who asked us, “How may I help you?”

Dali stared at her with his jaw hanging low and his eyes bulging out.

Xiaotao glared at him and showed the woman her badge. Then she roughly explained the whole situation to her. At first, she vehemently denied any association with Cheng Yahui. She was happily married, she insisted. But when she heard that she might be killed, her tone changed and she reluctantly admitted to having an affair with Cheng Yahui.

Xiaotao ordered a number of police officers to covertly surround the shop and we stayed in the shop under the guise of being her customers. The protection of the florist was not top priority—what was more important was to lure the murderer out to her.

The process of waiting was very boring. Bingxin looked around the shop and told me, “Song Yang-gege, I really like this white rose. Why don’t you buy me one?”

“You’re shameless, aren’t you?” Xiaotao sneered at her.

Bingxin stuck out her tongue at Xiaotao and replied, “It’s none of your business! I was just joking anyway!”

“Song Yang,” Xiaotao said to me, “it’s my birthday next month. I don’t want you to spend too much money on the present, so a single red rose will do.”

Bingxin was shocked and cried, “Why would he buy you a red rose? Only boyfriends or husbands gift red roses! Don’t you have any common sense?”

“Who cares?” Xiaotao snorted. “I like red roses and I want him to buy me one.”

“You… You’re abusing your authority! My dad will hear about this!”

“Is that all you can do? Crying to your dad? How childish!”

They stared each other down in anger. I was caught in the middle and it was getting really awkward.

“Maybe I can buy each of you a rose?” I suggested.

“No!” they both yelled.

“You guys really are police officers, aren’t you?” asked the florist.

“That’s rich, coming from you!” snapped Xiaotao. “You and your messy private life!”

“It’s not like I have any illusions about Dr. Cheng,” replied the florist. “I never felt real affection for that bastard. My married life is just so dull that I have to find someone to relieve my boredom, that’s all.”

I was surprised at how openly she discussed the matter.

“I wouldn’t mind if she finds me to relieve her boredom,” Dali whispered to me.

The florist overheard that and winked at Dali and said, “You look quite delicious, young man. You can come and chat with me whenever you’re free!”

Dali nodded eagerly and said, “Sure! I—”

I cut him off with a loud cough and glared at him.

At around noon, the florist said, “You’ve all been working very hard. I’ll order takeaways and we should all have lunch together!”

“Awesome!” cried Dali.

Xiaotao glared at him and told the florist, “No, thank you. We’re still on duty.”

The florist then ordered takeaway for herself. Once the food arrived, she tore open the packaging and was about to devour her food when I shouted, “Stop! Please let us check the food before you eat it.”

“Oh, I’m sure the food is fine!” said the florist. “I order their food every day, so I’m sure they wouldn’t do something so stupid like poisoning their own customer!”

“Today’s different,” I insisted. “Please let us check the food!”

We took samples of the food. Sun Bingxin opened her little box and started testing them. After a while, she confirmed that the food was safe.

“Ah, now the food has gone cold!” the florist complained.

After finishing the meal, she was about to light a cigarette when I stopped her again and said, “Wait! We have to check that too!”

“When will it end?” she sighed.