“Go downstairs and see if the light over the front door is working. And check if the stair gate is locked while you’re at it.”

Qian hovered for a moment, awaiting an explanation, but when none was forthcoming, nodded and said, “Sure,” and left the apartment.

Li stood for a long time, thinking, visualising. Eventually he wandered back into the living room and his eyes fell upon the bookcase again. As they drifted back and forth across the rows of multicoloured jackets, he recalled Mei Yuan’s riddle: Two men. One of them is the keeper of every book in the world, giving him access to the source of all knowledge. Knowledge is power, so this makes him a very powerful man. The other possesses only two sticks. Yet this gives him more power than the other. Why? And suddenly Li knew why. He smiled. How apposite, he thought. How strange. Perhaps Mei Yuan had psychic powers.

A tiny winking red light on the other side of the room caught his eye. He crossed to a small cabinet with an inset shelf. Set back on the shelf was a mini hi-fi stack with tuner, cassette and CD. Li crouched down to look at the array of pinpoint red and green lights, and a digital display of the numeral “9.” “Either of you guys touched the hi-fi?” he called through to the forensics men.

“No,” one of them called back.

“Me either,” the other one shouted.

Li looked up as Qian came back in, a touch out of breath. “Someone stole the lamp, boss. At any rate, there’s no lamp in the light fitting, and the old boy in the lift says it was working okay when he finished up last night. Oh, and the gate’s locked.”

Li nodded. “Know anything about hi-fi systems?”

“Got better things to spend my money on. In any case, I’d never have time to listen to one. Why?”

“Chao left his on. In fact, he left the CD on pause. The light’s still blinking. You want to hear what he was listening to when his killer came calling?”

“How do you know his killer came here?” Qian was curious.

“Educated guess,” Li said, and he pressed the Play button. Immediately the room was filled with the sounds of strange and alien music. He stood up and lifted an empty CD case off the top of the cabinet. “Western opera,” he said. And reading from the cover, “Samson and Delilah. Saint-Saëns.” He took out the inner sleeve. “Track nine. ‘Mon coeur s’ouvre a ta voix.’” And he read, “‘Samson, the champion of the Hebrews enslaved by the Philistines, knows that he should resist the approaches of the temptress Delilah. But his determination crumbles when she seduces him with this song of love. He yields completely, enabling Delilah to discover the secret of his strength and cut off his hair, rendering him powerless.’”