Then in October, the girl attended Thorpe Wood again but this time with her brother in tow. Turned out the bastard had done it to him too. Thomas Warren was arrested and informed of the additional allegation. A week later he walked into Peterborough Railway Station at 4 a.m., saving his children the distress of giving evidence and the public purse a great deal of money.

I hover by the wall to one side, reading what Lockhart is reading on his computer.

Thing is, until there was corroboration, Lockhart is thinking, he would have had his doubts about this one too – not because he is a cynical or disbelieving sort but because Thomas Warren seems like such a normal, regular guy. Lockhart thinks about his little niece, who he adores; the twin boys his cousin in Ruislip had in the new year, eleven months old they are now, and there’s a picture of them on the family’s Facebook page sitting in high chairs opposite each other clutching plastic spoons in their fat little fists and trying to feed each other. The idea that anyone could hurt a child, let alone his own child … doesn’t every fibre of your body scream against it? How is it physically possible? As he sits there, Lockhart shakes his head.

It is literally unimaginable, a man who looks just like his uncle or his cousin or his favourite teacher at school: it is so much easier to believe that a troubled young woman is a bit nuts. Some people just are, after all – like most police officers, Lockhart spends half his job dealing with people’s mental health issues. And it’s not like Warren was a TV celebrity or anything, when he reckons half of them are only jumping on the bandwagon in the hope of making a bit of cash off the tabloids – no, Warren was just a regular Joe, and that’s what makes it so hard to believe. Lockhart stares at the photo of Warren on the computer, his driving licence shot. He sits back in his chair and sighs; then he leans forward and picks up the phone.

When the number answers he says, ‘Can I speak to the Mortuary Manager?’

He’s on the phone to Peterborough City Hospital, which is where the mortal remains of Thomas Warren will be sitting in a fridge while his ghost continually enters the station, climbs the stairs, crosses the walkway, descends the stairs to Platform Seven and heads for the metal bench.

‘Hello, this is PC Lockhart from the British Transport Police …’ Lockhart explains he is calling to see if the pathology report is ready as he needs it to collate his information and send it all on to the Coroner’s Office.

A woman is explaining to Lockhart that the report is all ready, just needs printing up and putting in its folder.