Was it to the temptation of his drug habit, or his preference for young boys, that Chao Heng had yielded, leaving him powerless in the hands of his murderer? The voice of the female soprano rose in sensuous crescendos.

“So?” Qian was impatient. He had to raise his voice above the music. “What are you basing this educated guess on?”

“On a number of things,” Li said. “The first of them being that Chao Heng was almost certainly here last night.”

“How do you know?”

“The bath-towel hanging over the bath is still damp. He’d fed his fish, probably quite late on, because they’re still not that hungry. He’d left his cigarettes on the table on the balcony, and his needle kit in the bedroom. And smokers and junkies don’t leave those kinds of things behind. Not voluntarily. He didn’t leave by the elevator. There was no key among the effects found with his body, so how could he have locked the stair gate behind him?”

Li wandered back across the room to the balcony. “I think he was sitting here, listening to Delilah seducing Samson, and having himself a bottle of beer from the refrigerator. He had probably been here some time, judging by the number of cigarette ends in the ashtray and the progress of the CD. It was late, long after the lift had been shut down, maybe one or two in the morning, when the rest of the building was asleep. He was watching for a car below. A delivery of heroin, perhaps. The promise of a young boy. Who knows? When he saw the lights of the car, he got up, paused the CD, took his key and went down the stairs to unlock the gate. It would have been darker than usual, because the killer had just removed the lamp from the light over the front door. Maybe that’s why Chao didn’t recognise immediately that his visitor wasn’t who he was expecting.

“Whoever it was probably had a gun and forced him back up to the apartment. Once here, he struck him on the head with a blunt object, maybe even with the gun, and injected him with ketamine. He waited, maybe as long as an hour, to be sure he hadn’t been seen, then carried or dragged Chao down the stairs and locked the gate behind them at the bottom. Under cover of the darkness created by the removal of the lamp, he carried him the fifteen feet to where he’d parked the car. Then it was off to Ritan Park, and you can pretty much put the rest together yourself.”

By now Samson had well and truly succumbed to the charms of Delilah. Qian blew air through pursed lips. “That must be some education you had, boss.” He paused and thought about it. “How do you know the killer was acting alone?”

“I don’t.”