She felt horribly contaminated. She couldn’t bear it for another moment. She pulled her suit off and crammed it into the bin, then took off the rest of her clothes and pushed them into the washing machine. She stood under the shower and washed her hair and her body, scrubbing at it until she felt sore. She only stopped when the water turned cold. She rubbed herself down with the towel and dressed quickly in baggy jeans and a sweater.

She picked up her phone again and scrolled down. There: that was it. It was labeled Firework Night and had been put up by someone called Nico. It was almost unwatchable. People were dancing and it felt like the person filming them was also dancing. The image was juddering and shifting. It was nighttime and the dancers were either illuminated by the rippling light of the fire or turned into silhouettes. But Jude clearly recognized the faces of Danny and Vin and, she thought, briefly, Irina. Sometimes Danny seemed lost in the moment, her arms held above her head, moving to the rhythm. She was a beautiful, sinuous dancer. Another thing she’s good at, Jude thought to herself.

At one point, Danny noticed she was being filmed and gave a broad smile and said something inaudible. The little film lasted just under fifteen minutes, but there were repeated cuts and the music changed. Danny was seen over and over again.

When it was done, Jude thought for a moment. She rang Leila Fox.

“I watched the film,” she said.

“Good. You didn’t really need to ring and tell me that.”

“There are gaps,” Jude said. “Cuts.”

“What do you mean?”

“There are gaps in the film. She could have been filmed and then left the party and then come back and been filmed dancing again.”

“Please,” said the detective.

“Isn’t that true?”

She heard a deep breath being drawn.

“I don’t need to justify myself to you, Jude. But just this once: the party in question was in Brixton, which is a long way from the marshes and would have taken Danny a good hour to get to. Multiple witnesses attest to her arriving shortly after five forty-five, which was when the fireworks started. A colleague watched the full version, which is time-coded and extends over a period of more than two and a half hours, between six p.m. and eight-thirty p.m. Danny Kelner is repeatedly visible.”

So Danny’s alibi covered almost exactly the stretch of times during which the pathologist had said Liam had died.

“It’s possible she could have left and returned,” Jude said lamely.

“It’s not possible.”

“Don’t you think it’s a bit convenient?”

“What?”