It took less than forty minutes for DCI Seawoll to reach Downshire Hill. Even with the Saturday traffic it meant he must have been doing blues and twos all the way from Belgravia. He appeared in the side doorway of the van and frowned at Lesley and me.

‘You two all right?’ he asked.

We both nodded.

‘Well, don’t fucking go anywhere,’ he said.

Fat chance of that. A major investigation, once it gets under way, is as exciting as watching reruns of Big Brother, although possibly involving less sex and violence. Criminals are not caught by brilliant deductive reasoning but by the fact that some poor slob has spent a week tracking down every shop in Hackney that sells a particular brand of trainer, and then checking the security-camera footage on every single one. A good Senior Investigating Officer is one who makes sure their team has dotted every I and crossed every T, not least so that some Rupert in a wig can’t drive a defendant’s credit card into a crack in the case and wedge it wide open.

Seawoll was one of the best, so first we were taken out separately to a tent that the forensic people had erected near the front gate. There, we stripped to our underwear and traded our street clothes for a stylish one-piece bunny suit. As I watched my favourite suit jacket being stuffed into an evidence bag I realised I’d never bothered to find out whether you ever got things like that back. And if they did give it back to me, would they dry-clean it first? They took swabs of the blood on our faces and hands and then were nice enough to hand us some wipes so we could get the rest off.

We ended up back in the transit van for lunch, which was a couple of shop sandwiches, but this being Hampstead they were pretty high-quality. I found myself surprisingly hungry, and I was thinking of asking for a second round when DCI Seawoll climbed into the van with us. His weight caused the van to sink down on one side, and his presence caused Lesley and me to push ourselves unconsciously into our seat backs.

‘How are you two bearing up?’ he asked.

We told him that we were fine and ready, in fact dead keen, to get back up on that horse and go to work.

‘That’s a load of wank,’ he said, ‘but at least it’s convincing wank. In a couple of minutes we’re going to take you down Hampstead nick, where a very nice lady from Scotland Yard is going to take your statements – separately. And while I’m a believer in veracity in all things, I want to make it clear that there isn’t going to be any fucking mumbo-jumbo voodoo X-Files shit in any fucking statement. Is that understood?’

We indicated that he had indeed adequately communicated his position.