An old black-and-white photograph, turned yellow and brittle from the damp — three people in the image: a middle-aged man seated in the center, flanked by two girls wearing matching dresses.

The taller girl had long hair falling to her waist, her features delicate and pretty, smiling brightly at the camera. The shorter girl was turned slightly sideways, one side of her hair covering half her face, as if she were a little shy.

“You Xiaozhen,” Shi Ting said with certainty. “This photograph appears to be six or seven years old.”

Bai Jin did the mental calculation — if it was five or six years ago, You Xiaozhen would have been only twelve or thirteen. Then the smaller girl on the right must be…

“Her hair covers her face, but if you look closely, you can still see traces of a blue-green birthmark beneath the strands. That should be Jing Lan.”

“So it matches what that neighbor said — You Xiaozhen had two family members: the man in the center is her father, and the girl beside her is her sister.”

Shi Ting placed the photograph into an evidence bag, then picked up a small glass medicine bottle from the desk. It was one he and the others knew all too well — the source of all this evil: WAKAWOTO Stomach Powder.

He then pulled open a side drawer. Beneath several layers of newspaper, a row of identical bottles sat side by side. He examined the batch numbers on each in turn, then said quietly, “The batch numbers match the ones Qiao Guang collected from her work unit. This confirms these are the stomach medicine tablets that went missing before Qiao Guang’s death.”

The batch numbers were a combination of letters and numerals — two letters followed by eight digits in each set, with no discernible pattern. Yet he had memorized them all after a single glance.

Bai Jin was long accustomed to his commander’s formidable memory and showed no particular surprise.

“Well, that’s conclusive evidence.” He couldn’t help but let out a low whistle.

“The evidence doesn’t end with these medicine bottles.” Shi Ting found a paper-wrapped glass syringe in the drawer. It was noticeably twice the length of the largest syringe available on the market — its seams were clearly visible where pieces had been joined, and black adhesive tape was wound around the connection point.

Shi Ting recalled that Yan Qing had said the killer injected air into the victims’ armpits. More than 100 milliliters of air entering the bloodstream was enough to kill. The killer had clearly already determined the lethal dose and, wanting to succeed in a single attempt, had crafted this custom syringe.

“Strange — there’s no gun anywhere.” Bai Jin searched the room. “The victims were forced to swallow cotton and tacks, and were struck across the face with a ruler. Even as they were being killed, they didn’t resist. If the killer had no weapon with which to intimidate them, that doesn’t add up.”

The inconsistency Bai Jin raised was the very thing Shi Ting had been unable to work out. He felt they had still missed an important clue.

By all logic, Jing Lan was a poor student who could barely support herself — there was simply no way she could have obtained a firearm. So what had she used to compel three victims to submit and accept their deaths willingly?

“Have you found anything?” Yan Qing’s voice floated down from above, anxious and tense.

Shi Ting tilted his head back. “There is evidence, but certain questions still need corroboration.”

Although she had anticipated this outcome, hearing the word evidence, Yan Qing couldn’t help but let out a quiet sigh.

Even now, she could not reconcile the warm and sunny Jing Lan she had known with a cold-blooded killer who took lives without blinking.

“What is this?” A startled shout came from the corner. “Nearly gave me a heart attack.”

Bai Jin was standing in front of the iron clothing rack, holding up a dark, shapeless mass, the alarm on his face not yet entirely faded.

—