“It’s not common practice to destroy evidence in China either,” Li said. “In this case, it seems, authorisation to destroy the remains came as the result of an ‘administrative error.’” It had taken him all morning to track that one down. They had even shown him the form. A clerk had typed in the wrong name, they said.

She shook her head. “And you believe that?”

“No.” He closed his eyes and breathed deeply, keeping his anger in check. “Someone’s gone to a lot of trouble to cover their tracks. But there is one loose end.” He paused. “You.”

“Me?”

“You requested the AIDS test from Professor Xie last night—long before he received instructions to destroy the body and the samples.”

“But if he’s denying that . . .”

“That’s why I’d like a sworn statement from you before you leave. I know it’s only your word against his . . .”

“But it’s not,” Margaret said. “There was a witness.”

Li frowned. “Who?”

“Lily Peng. She insisted on coming in with me when I went to talk to Professor Xie.”

Li processed his thoughts rapidly. “Well, there’s no way he can get around that one, is there?” He ran it through again in his mind. “And that means I can use you and Lily to frighten him. Sometimes when rats are scared they squeal. Do you still want to go and see him?”

Margaret hesitated. It would be too easy to say yes, to get involved again, let all that emotion back in when she’d just spent the last three hours building resolute defences against it. “I don’t think the university would approve,” she said feebly.

“This has nothing to do with the university. You’re a material witness.”

“So . . . I don’t have any choice. Is that what you’re telling me?”

“That’s what I’m telling you.”

“Then I don’t have any choice, do I?” There was just the hint of a smile about her eyes.

He grinned. “No,” he said. “You don’t.”

It took less than fifteen minutes to drive to the Centre of Material Evidence Determination. For the first five neither of them spoke.

Margaret was having immediate regrets. She knew perfectly well that she could have refused to get involved, and Li would not have forced her. She had been foolish. What could possibly come of this but trouble and heartache? Nothing had changed. She was still leaving on the nine thirty flight in the morning. She would never see Li again. She would never return to China. What did she care about the murder of Chao Heng and some drug dealer and an unemployed labourer from Shanghai? What did it matter to her that someone was trying to block Li’s investigation? Who cared?

Li said, “We’ve identified the killer from that thumbprint.”

And she knew that she cared. She couldn’t have said why, only that she did. “Who is he?”