‘I understand nothing of the sort,’ he said, but he unconsciously slipped his right hand, with its fresh bandage, out of sight under the table. He’d worn fingerless gloves at the Tate Modern, not an affectation but a disguise.

‘We have the wounds on your hand which match the murder weapon. In twelve hours we’ll have the DNA results which will match the swab you gave ten minutes ago to the blood we found on the aforesaid weapon.’ I paused to let that sink in. ‘As soon as we knew there were other entry points into the system we pulled the CCTV footage from cameras around Bayswater and Notting Hill. Sooner or later we will break your alibi.’

According to HOLMES, Ryan Carroll had been statemented the day after I’d met him and had been given an alibi by one Siobhán Burke, who claimed to have been sleeping with him on the night in question.

‘Whether or not Ms Burke faces charges of aiding and abetting after the fact,’ I said, ‘rather depends on the outcome of this conversation.’ That was an outright lie. Stephanopoulos would be using the threat of a perjury charge to get Siobhán Burke to flip on Carroll but we figured that he’d respond better if we thought he was the centre of attention. We’ll use your ego against you if we can – we’re not proud.

This approach, trying to roll over your suspect before their lawyer arrives, is high-risk and I could practically hear Seawoll grinding his teeth from next door where he was no doubt monitoring the interview. I suspected that Stephanopoulos was also watching, and definitely Nightingale and probably Agent Reynolds, in which case Kittredge would be there to keep an eye on her. For an interview that wasn’t officially taking place there weren’t half a lot of witnesses.

‘That’s low,’ he said. ‘Even for the police, that’s low.’

‘My point, Ryan,’ I said, ‘is that we don’t need anything more to send you down. But we do want to know why. So we’re giving you this opportunity to get it off your chest and satisfy our curiosity.’

‘You want to keep this secret, don’t you?’ he asked. ‘I don’t suppose there’s a deal on offer?’

‘No such luck.’ I said. Seawoll had made that much clear.

‘What if I was to threaten to use it as part of my defence,’ he said. ‘Have it all out in open court. Try keeping your secrets then.’

‘You can give that a go if you like,’ I said. ‘Strange little men living in the sewers, keeping pigs and making pots? My money’s on you ending up in Broadmoor with a thorazine drip.’