‘Yeah, I was thinking the same.’ Lightman gave a very short sigh. ‘It’s so rare to have a weapon that might be traceable. It’d be supremely shit if it came to nothing.’

‘Supremely,’ Hanson agreed, and left the building feeling a little better about everything for some reason.

After some time spent banging on the door, Hanson had at last been shown into the cluttered office at the kebab shop and let loose on its old desktop computer. The hard drive had all the shop’s CCTV footage, broken down into three-hour chunks.

She sat on the battered foam of the chair and loaded up the file from twelve a.m., wondering what sort of view they were going to get. The answer was, unfortunately, not a great one. The camera was placed at the door, and pointed downwards fairly steeply to catch the faces of everyone coming in. The view of the pavement was limited to a distance of about twenty feet along, and to the near side of London Road. Anyone walking on the other side wouldn’t be caught at all.

She scrolled through to one thirteen and then hit play. To her relief, Louise Reakes entered the frame after two minutes. Hanson noted the time down and added a comment that Louise looked as drunk as she had on the nightclub footage. She had the unmistakable straight-legged gait of someone who was having trouble balancing, and in the few seconds of footage they had she veered sharply from left to right.

Hanson wondered if Louise might have been so out of it that she could have gone too far in defending herself. Though whether she could have been coordinated enough in that state to take a knife off someone and stab them was less clear.

Hanson started the video again, guessing that Alex wouldn’t be far behind Louise. He’d been less drunk. He was probably walking in straight lines.

And there he was, coming onto the screen seventeen seconds after her. Hanson immediately froze the clip, and wrote the time down with a suddenly accelerated pulse. On the still she had, he was moving aside to let someone out of the kebab-shop door, but his gaze was fixed down the street. As if he was looking at Louise.

Hanson breathed out, and then pressed play. Alex began to move again, and then unexpectedly faltered. His hand went to his pocket.

Hanson found herself fixated. Were they about to see the knife, and end all speculation over whose it had been?

His hand emerged, but it was holding something smaller. Something concealed easily by his palm. Hanson refroze the image, trying to tell what it was, but it wasn’t clear enough. It was definitely too small to be his phone.