'I'm telling you the truth,' he spluttered desperately. 'I swear it.'

I took a punt. 'What about those girls who went missing from Coleman House, Kover? What about them?'

'Look, I don't know-'

'You've got ten seconds to start talking. Otherwise you burn.'

'Look, please-'

'Ten, nine, eight, sev-'

'All right, all right, I'll tell you!'

I flicked off the lighter and stood up. 'It had better be the truth this time. Because otherwise I start the counting again at seven. Maybe even five. I'm tired of being fucked around.'

'All right, all right.' He paused for a moment to compose himself, then opened his mouth to say something. Then stopped. I think I knew then that it was going to be very bad. 'Me and Dr Roberts… we had a little business going.'

'What kind of business?'

'Girls. Young girls.'

I dragged hard on my cigarette, feeling full of dread. 'Tell me how this business worked.'

There was another pause while he thought about answering. In the end, though, he knew, like I knew, that he had no choice. 'I had a client, a bloke who wanted young girls. Except, the thing was… he wanted them permanently.'

'What do you mean?'

'He wanted girls who weren't going to be missed.'

'Why? What was he doing with them?'

'Well, you know…'

'No, I don't know. Tell me.'

'I think he was killing them.'

'Why? For kicks?'

'I think so, yeah.'

In my time as a copper, I'd come across cases where paedophiles had murdered their victims. Sometimes to make sure they couldn't tell anyone what had happened, but more often than not because the act of murder served to heighten the pleasure of the sexual act. Killing while coming. There are some people in this world for whom that's the ultimate thrill.

'Jesus.' I shook my head, trying to take it all in. 'So how did it work?'

'Dr Roberts would pick the girls, the ones he thought could disappear without it getting noticed, ones he was treating. He'd give me the rundown on their movements, tell me the best time and place to snatch them, then I'd do the rest.'

I stared at him, feeling sick. 'And how many times did you do this? How many girls disappeared?'

'We didn't do it much.'

'How many?'

'Four altogether.'

I dragged hard on the cigarette. 'Over how long a period?'

He thought about it for a moment. 'I don't know, about eighteen months. Something like that. The girl – the whore – she got a sniff of what was going on. Dr Roberts chose one of her mates for taking, and somehow she rumbled it. That's when she started blackmailing him, saying she'd expose him to the cops unless he paid her.'

'Did you know the name of Fox's friend? The girl Roberts… picked?' I found the last word difficult to say.

He shook his head. 'No, no. I never knew their names.'

'It was Molly Hagger.' He looked back at me blankly. 'Her name was Molly Hagger, and she was thirteen.' He looked down at his hands again, not saying anything. 'And Miriam Fox had to go because she was threatening to go to the cops?'

'Yeah. I picked her up pretending to be a punter. Then I did her.'

'I know. I saw the body.'

I stood there for a long moment, trying to digest what I'd heard, wanting at the same time to throw my guts up until there was nothing left. I have never felt so sick and depressed, so weary of it all, as I did standing there in that cramped little room with this fucking monster.

'And who was the last one you took? Was it a girl with black hair about the same age?'

'No. That girl, Fox's mate…'

'Molly. Her name was Molly.'

'She was the last one. The client didn't like us doing it too often. Otherwise it raised suspicions.'

Which left another mystery. What had happened to Anne Taylor? Although that one at least would have to wait for another day.

'And this client of yours, what's his name?'

Kover looked me right in the eye.

'Keen,' he said. 'Raymond Keen.'

I tried hard to hold in the shock that smacked me right between the eyes. Raymond Keen, a man I'd known for seven years, a man I'd killed for, involved in something so terrible that just the briefest thought of it made my skin crawl.

'I know Raymond Keen,' I told him. 'It doesn't seem his style to kill kids in some sort of sex game.'

'Why would I lie?' he answered, which at this juncture was a fair point. 'He's the client. I don't know if he's getting the girls on behalf of someone else.'

I thought about it for a moment. Raymond, after all, was a businessman. It was difficult to believe that he could be involved in a business quite so base and sick as the planned murder of children, but in the end no more difficult to believe than the involvement of Roberts, whose job it was to look after the mental welfare of kids, and I had no doubt that Kover was telling the truth about his part in all this. There was, I suppose, a ruthless logic in it all. Somewhere out there there were people – hopefully few, but who could tell – who got their sexual thrills from killing kids. Perhaps Kover was right, and Raymond was simply tapping into this vile market, using kids whose disappearance wasn't going to attract much attention. And like all his ventures he was keeping as far away from the action as possible. It was easy to see why and how he'd recruited someone like Kover, who was never going to have any sort of moral problem about sending kids to their deaths. But Roberts? That was far more difficult to swallow.

'So, where's Roberts now?'

'I had to tell Mr Keen about what happened with the other woman, that I'd had to kill her. He was worried about Dr Roberts letting stuff slip and giving the game away, so he got me to do Roberts as well. Just to stay on the safe side.'

'How did you kill him?'

'I asked to meet him last night to discuss things. I picked him up outside his flat. When he got in the car, I just leaned over and stuck a knife in his guts, then locked the doors. Then I drove up to Mr Keen's place. He said he'd take it from there.'

'You have been busy these past few days. So, Mark Wells-'

'Who?'

'The man who's been charged with the murder you committed. Or one of them, anyway.'

'Oh yeah, the pimp.'

'Was he involved in any way?'

Kover shook his head. 'No. He had nothing to do with it.'

'So how did you manage to set him up?'

'Dr Roberts did it. At first he wasn't going to bother, but he got cold feet when you lot came knocking. He said you came to Coleman House asking questions. I think it spooked him a bit.'

'How did he get hold of Wells's shirt?'

'It was in the girl… Molly's possessions. She told him once that the shirt reminded her of him. I think she was in love with the bloke or something. The possessions were still at the home, so Dr Roberts just took it out and planted it. He was cunning like that. Then he phoned, put on a woman's accent, and tipped off you lot.'

I remembered his pleasant sing-song voice. If anyone could have impersonated a female, it would have been him. Bastard.

'What about the knife?'

'He'd heard from girls at the home that this Wells liked to threaten people with a big butcher's knife. That's what I… that's what I killed her with. I kept the weapon, and just to, you know, fix him up perfect, Dr Roberts planted it near his place.'

'And that was that.'

'That's how it happened.'

'Raymond supplies you with a mobile, right?'

He nodded. 'Yeah.'

'Where is it?'

'Why? What do you want it for?'

'Don't fuck me about, Kover. You're the one who's tied up and drenched in petrol. Where is it?'

'In my pocket.' He just about managed to pat the outer pocket of his coat.

I stepped over and removed it, switching it on. 'I'm going to dial Raymond's private number now. When he picks it up, you're going to tell him you want a meeting with him as soon as possible. Preferably tonight. I expect he'll be reluctant. Don't worry. Be aggressive. Insist. Get a time. Make sure you definitely get a time. And don't give a fucking thing away. Understand? You fuck this up and you'll burn like a piece of charcoal.'