On the drive over to Chao’s apartment, Li hadn’t said a word, his thoughts, she assumed, filled with concern for his sister and the mission his uncle had undertaken at the behest of his father. Now, at Chao’s apartment, he seemed moody and unfocused. Margaret knew only too well how difficult it could be sometimes to concentrate on work when personal problems preyed on your mind. She knew she needed to shift his brain back into gear. “So you think he was sitting out there on the balcony,” she said, “waiting for his late-night caller?” Li nodded. The bottle of beer and the cigarette ends in the ashtray were still there. “And the CD is where?”

He crossed the room to the mini hi-fi stack and saw that the forensics boys had forgotten to switch it off.

“Do you want to put on the track that was playing?”

He shrugged and whizzed through the tracks to number nine and pressed play. As the soprano’s voice soared through the apartment, Margaret wandered to the bookcase and ran her fingers along a line of books with familiar titles. Plant DNA Infectious Agents, Risk Assessment in Genetic Engineering, Plant Virology. Titles that had lined Michael’s bookshelves at home. The same titles that had seemed so alien to Li just twenty-four hours before. She slipped her hands into the neatly tailored pockets of her dress and moved out on to the balcony. She looked at the empty beer bottle, the pack of cigarettes, and wondered what he had lit them with. Then remembered the Zippo lighter among his effects. And something began happening in her mind, something spontaneous, a sequence of electrical sparks making connections that would never have occurred consciously. All that data that the brain holds in limbo, accessed by some pre-programmed instinct. She could taste the jian bing, the salty sweetness of the hoi sin, the burn of the chilli, the sharpness of the spring onion. And she saw Mei Yuan’s round, smiling face. She wheeled round to see where Li was. But he had left the room. She hurried into the hall and called his name. “In here,” he said, and she went into the kitchen.

“Mei Yuan’s riddle,” she said.

He looked at her blankly. “What about it?”

She shook her head in frustration. “It’s just a thought process. Bear with me.” She fought for the words. “The man with the two sticks. If he was going to burn the books, he would do it for a reason, right?”

“To destroy them.”

“Exactly. So the keeper of the books couldn’t access them. He would have no way of knowing what was in them.”

Li shrugged. “So?”

“So why set Chao Heng on fire?”

“To make it look like suicide.”