Ouyang was out for a meeting. Chen asked some questions of Meiling instead, who seemed to be evasive, hemming and hawing, unwilling to look him in the eye.

He checked his watch. Already near twelve. It was not a day for him to spend hours on questions that seemed to be leading nowhere.

So he was ready to leave the association for the preview in the New World.

After lunch, after selecting the pictures, after sending a text message to Peiqin, Detective Yu asked Detective Qin over to his office.

With Qin focusing on the number four victim Xiang, Yu began by raising the point about her mask and cake that morning, ready to bring up Inspector Chen’s analysis for support. He had hardly got into any details, however, when Qin brushed it aside, waving his second finger.

‘We have noted that, Inspector Yu. But it was more than a block – not just several steps, as you have said – from the Wenhui building to that snack stall. So it made sense for her to pull on a mask to go there. As for the incompatibility of eating the cake and wearing the mask at the same time, Xiang could have worn the mask with just one of its straps on while biting at the cake in her hand. You may have seen young people doing that on the street. Sort of rakish among them. Nothing to wonder about.’

‘Yes, it could have been like that,’ Yu said, admitting to himself that he should have thought of the possibility. As a result, he found himself at a temporary loss as to how to go on discussing the other issues of the mask.

And Qin was already standing up. ‘I’m going to a meeting with Internal Security again. I’ll keep you posted. Don’t worry about it, Inspector Yu.’

The moment Qin was out of the office, Yu began dismissing the scenario of her having the mask on with only one strap.

A young woman like Xiang could have done that. It sounded plausible in theory – but far-fetched. Yu started pacing about in the cubicle alone.

Some of the details of Inspector Chen’s analysis came back to him. It would have been messy to eat the sesame-strewn cake from one’s hand, not to mention the oily fried dough stick. If Xiang had kept the mask on with one strap, letting it dangle over her cheek, it could have been easily smeared, unwearable afterward.

His cellphone buzzed. It was a text message from Peiqin in response to his sent before the discussion with Detective Qin.

‘I’ve just talked to Lianping again. Here’s one detail from her about the mask – if that’s what you’re really focusing on.

‘The snack stall is nearby. No need for a mask with such a short distance, at least that’s Lianping’s take. When Xiang walked out that morning, neither her colleagues in the building nor the doorman at the entrance remember seeing her wear a mask. Besides, Lianping has never seen anyone wearing a yellowing mask in Wenhui. She checked with Xiang’s colleagues in the same section. The same impression.’