“I was at the end of the car when she passed me with it on the way out. I said, ‘Maybe you should leave a receipt or something.’ She laughed and showed me her badge again,” he explained, turning to look down the platform. The engineer was shouting for him from beside the locomotive. Obviously relieved for the excuse, the conductor mumbled an apology and hurried away.

As Shan watched him retreat, a lanky figure stepped off the train. The conductor apparently muttered something to the man as he passed him, for his head snapped around in Shan’s direction. He seemed to groan as Shan held up a hand for him to wait.

“What good fortune to see you, Doctor,” Shan said in greeting.

The doctor did not share the sentiment. “I have to report to the office,” he said impatiently.

“Fine, we can go there together and I can speak to the train master, so I can explain that you can’t make the next train because law enforcement needs you.”

The doctor sighed. “What is it you want, Inspector?”

“The autopsy report for Sun Lunshi. You never sent it to me.”

“I gave it to the Public Security officer who followed up for you. Lieutenant Huan, Lhasa Division. He said he would get it to you. Hardly worth the trouble. It just confirmed my initial findings. We hand out warning brochures to every passenger. We can’t be responsible when people don’t read them.”

“I don’t follow.”

“He inadvertently killed himself. His levels of benzodiazepine were off the chart.”

“A drug?”

“A sleeping aid. It’s a long trip, a stressful and restless night for many. We tell passengers to never take such drugs on the sky train. It inhibits breathing, lowers blood pressure. Combine that with even a moderate case of altitude sickness and the results can be fatal. You saw his blue fingers, his cyanosis. The fool didn’t have a chance. He took too many pills, fell asleep, and never knew he was shutting his eyes forever.”

“Tell me something, Doctor. Could a few pills like that be mixed in with soda and swallowed?”

“Of course. They’re small pills, hardly noticeable in a swallow of soda. Or if given a few moments to dissolve, not noticeable at all.”

Shan glanced at a passing knob patrol and thanked the doctor. He willed the doctor to walk away, then gazed with new understanding at the shiny, serpent-like machine beside him. The sky train was a murderer’s paradise.

“It’s not your fault, Shan,” Pike said. They had been sharing a pot of tea as Shan explained what he had learned.

Shan looked up from his cup. “What do you mean?”