Gillard carefully removed the blood-tainted book. In the gloom he couldn’t see the title, so he retreated to the entrance to turn on the light. A Pictorial History of the Bridges of London, it was called. The paper dust jacket was ripped, but it wasn’t too old. Published in 2012. Looking inside the frontispiece, Gillard could see a pencil mark giving the price. It looked to him like a charity shop buy.

‘Pass me a large evidence bag,’ Gillard said. ‘I like to see if we can get any dabs off this. Perhaps you should take a selection of the other books as well.’

‘That’s good thinking. I’m going to dig out some samples of these stains for analysis. There’s a process now called real-time reverse transcriptase PCR which can work out how old bloodstains are based on the degradation of the RNA in the blood. It came up in my forensic course. The crucial issue is the sample size. I’m not sure the single drop of blood on the spine of a book will be enough, and the bleach-treated droplets that BlueStar picked up may not work at all. But I’m going to try.’

‘Hold on, Kirsty. Make sure you leave enough from that single drop to allow a test to see whether Ozzy was the victim here. That’s the priority test.’

They both looked at the book. A single drop of blood, the kind you might get from a pinprick, and so much was riding on it.

‘Okay.’

‘And Kirsty, I’d like you to be in on the next interrogation of Rev Cleaver, tomorrow morning when we put the evidence to him. I’m having him re-arrested.’

Gillard didn’t get back to the office until six. Research Intelligence Officer Rob Townsend was sitting at his desk, phone clamped under his chin as he liaised with the service provider to get a trace on the phones that had recently rung Vicky and Rowena Willow.

‘How you getting on, Rob?’ Gillard asked, after the call ended.

‘Not too bad. I’m tracing Crystal’s phone now. I’ve also got Vicky and Guy Naylor’s mobile phone numbers from their own pub website. We’ll get the metadata back, probably by ten tonight. To save you some time, I filled out the warrant form so we can see the contents of messages. The duty magistrate is in Oxford this evening.’

‘That’s good work.’

‘We already have the metadata from Matthew Cleaver’s phone, so I could identify Rowena Willow’s phone number from that. She seems to ring him about twenty times a day.’

Gillard nodded. ‘I think she’s besotted with him. I just hope he hasn’t done anything about it. She only had her sixteenth birthday six weeks ago.’

‘Ah, I see,’ Rob said, his pale ginger eyebrows flexing. ‘We might find out once we get to see the texts and voicemails between them.’