Chen laughed heartily, to the amazement of the detectives who could hear him through the open door. He steered Margaret out and into the corridor, followed by a resentful Lily. “Come, I will see you to your car. And I will phone Professor Jiang this afternoon to thank him personally for letting us borrow you.”

Margaret flicked a backward glance over her shoulder to see Li already involved in discussions with his detectives. In all likelihood she would never see him again.

As she turned to be led down the corridor, Li looked over to the door to see her back for an instant before she disappeared. Apparently, he thought bitterly, he wasn’t even worth a backward glance.

Another couple of sullen hoodlums were bundled in to have details taken before being led away for interrogation. “We took more than fifteen statements this morning,” Wu told Li. “Anyone and everyone who knew Mao Mao. The scum of the earth. Dope dealers, pimps, prostitutes.” Li wandered through to his office and Wu followed. “He wasn’t a very nice guy, Li Yan. Nobody’s shedding any tears for him. Even his family. You’d think a mother would grieve for her son. When we told her, she just spat and said, ‘Good riddance.’”

From his window, Li could see into the street below. Through the foliage he watched as Margaret got into the BMW. Good riddance. Mao Mao’s mother’s words about her son found an echo in his present thoughts. Just before she closed the door, Margaret glanced up. Damn! She’d seen him watching. He took a quick step back, then felt foolish. This was absurd! He focused his mind again on Wu, who was still talking. “It was definitely drugs he was into, but he wasn’t one of the Golden Circle, just one of the flies attracted by the dung.”

The Golden Circle was what they called the ring of dealers at the centre of the Beijing drug trade, the ones whose hands were always clean, who always had an alibi, who never took the rap. They were the ones who made the money, trading death for gold.

“Of course,” Wu said, “no one knows a thing.” He paused. “And you know what, boss? You get an instinct for these things. I don’t think they’re lying.”