“From within,” Old Yifu said. “From what you know.” He paused thoughtfully. “Tell me again about the way Chao Heng’s killer went about his business. In the apartment, and in the park.”

Li went through it all, replaying his thoughts, all the tiny clues, the moments of discovery and illumination. The CD still paused in the player. The blood on the carpet. His vision of the killer carrying the body downstairs and out into the darkness created by the removal of the lamp. The daring murder in broad daylight, Li’s vision of the killer walking nonchalantly from the park even as the blazing body of his victim was being discovered.

“And what does this tell us about the killer?” his uncle said. Li shrugged. “It tells us that he is a clever man who planned and executed this murder with a professional precision. In the normal course of events, you would never have discovered that his victim had not committed suicide. He could not have known that a visiting American pathologist, expert in the post-mortem examinations of burn victims, would be invited to perform the autopsy. For all our growing expertise in China, we still have a long way to go. Not many of our pathologists would have identified the fracture of the skull as anything other than a heat fracture. Very few of our pathologists have the experience of drugs that would have led them to guess at the use of a sedative—this . . . ketamine—on top of a heroin habit.” He stopped, mobile eyebrows pushed high on his forehead, looking for an acknowledgement from Li.

“You’re saying the killer was a professional?” Professional killers in China were a very rare breed of animal. “In Beijing?”

“Oh, he would have come from Hong Kong probably. ‘One country, two systems.’” His smile reflected a certain irony. “Some Triad hit-man.” Old Yifu jabbed a finger in Li’s direction. “These other two killings. No clues left at the scene. One is killed by a single thrust of a knife up through the ribcage and into the heart. The other by a clean break of the neck. These were no casual killings, Li Yan.”

Li’s breathing had become shallow. More rapid. He fought to make sense of it. “If they were professional killings, then that establishes a link beyond the cigarette ends.” He shook his head, still perplexed. “But why? Why would someone employ a hit-man to kill a retired adviser in agriculture, a nobody drug dealer, and an unemployed labourer from Shanghai?”