'I don't know what you're talking about,' he blustered, looking down at his hands. 'Honestly.'

I pushed the tape back, then turned and walked into the kitchen, picking up the freshly boiled kettle.

He knew what was coming when he saw me emerge with it, but there was nothing he could do. Desperately, he struggled in the seat as I stopped in front of him, stood there for a moment, then ever so gently tilted it until the boiling water dribbled slowly out and onto his upper left thigh. I increased the flow a little, moving to his other leg, watching as his face stretched tight and red with pain and his eyes bugged out of his head. I stopped, paused for maybe three seconds, then repeated the procedure, this time chucking a little on his groin for good measure. His wriggling became hysterical and a surprisingly loud moan came from behind the tape as he tried to cry out. His face was now beginning to go purple.

I stood back and watched him for a little while, a serene smile on my face. I felt that I was performing a worthwhile task, probably the most worthwhile task I'd performed in my whole career.

Without warning, I chucked a load more over his groin, waited while the pain racked through him in great agonizing bursts, then put the kettle down and took a drink from the beer.

'Right. I hope we understand each other now. There's no limit to the pain I'll inflict on you if you don't answer my questions truthfully, so it's in your interests to just get it over with. And in case you think about crying out…' I reached down beside the chair to where the small jerry-can of petrol sat and poured its contents all over his body and head. 'If you thought hot water was painful, then nothing will prepare you for this.'

I put the can down and removed the tape. This time I crumpled it up and chucked it on the floor. I was confident I wouldn't need it again. He'd answer my questions now all right. Kover gritted his teeth, still fighting against the effects of the scalding, and turned uncomfortably in his seat.

'Now, let's start again. Carla Graham was involved in the murder of Miriam Fox. I know that for a fact. And I suspect you were too. What I'm missing is the reason. Whatever it was, you and her fell out about it, and you responded by butchering her on her own bed. Now, let me tell you something. There's no point in you not telling me the whole truth or protecting anyone else who may be involved or whatever, because if I get one word of a contradiction in your answers, then you'll burn. It's as simple as that. And I know you know that I'm serious.'

'Look, I didn't even know her! She was just-'

I pulled a lighter from my pocket and stepped forward, igniting the flame so it was only inches from his petrol-soaked face. Instinctively, he turned his head, but I followed it with the lighter and the flame remained right in his field of vision. He let out a fearful moan.

'You know, Kover, you're a very slow learner. I know you knew her. There's no way you got through the security door into her building without being let in, and there was no forced entry to her flat because I was there just after you, remember? You knew her and, for whatever reason, I think she was expecting you. So, I'm going to ask again: why did you and Carla murder Miriam Fox, and why did you then kill Carla?'

There was a long pause. The moment of truth. It was like opening a door, although even in my darkest nightmares I could never have been prepared for what I heard that night.

'I killed her. The one last night. But I didn't know her, I swear it.'

'Then what did you kill her for?'

He sighed, his face still reflecting the pain he must have been in. 'Because I was told to.'

'By who?' He didn't say anything. 'By who, Kover? There's no point protecting anybody here, you know. Not in the position you're in.'

'This bloke who worked with her. He was the one who told me to do it.'

'What's his name?'

'Dr Roberts.'

'Dr Roberts, the child psychologist? The guy from Coleman House?'

'Yeah, him. That's how I got in the flat. He had keys. I think he took duplicates.'

I was confused. 'What did he want her dead for?'

'She was on to him for something.'

'And what was that?'

'Look, it's all a bit complicated.'

'I don't care how complicated it is. Start talking.' I flicked on the lighter again, just to remind him that I wasn't fucking about. It had the desired effect.

'She knew he'd had something to do with the murder of the whore. The one you lot found last week down by the canal.'

'Miriam Fox?'

He nodded.

'You killed her, didn't you? Miriam Fox.'

'Yeah, I killed her,' he said eventually.

'So, Carla Graham had nothing to do with the murder?'

'No.'

I felt an overwhelming gloom then. Guilt sank slowly down onto my shoulders. Guilt that I had seen only the worst in her. That I'd misjudged her, and that her anger at my false accusation had been genuine. And that, in the end, I'd done nothing to save her.

'How did Carla find out about Roberts's involvement?'

'I don't know for sure, but I think he told her something only the killer could have known, and for some reason she picked him up on it yesterday.'

So that was how she'd known the manner of Miriam's death. Roberts must have let it slip while talking to her. I felt another terrible pang as it became clear that, by confronting her in the Gallan, I'd effectively signed her death warrant.

'And so he called you to sort it out?'

He nodded again, not looking at me. 'Yeah, that's right.'

'So how did a respectable child psychologist know a convicted lowlife paedophile like you? How did he know you so intimately that he could call upon your help to commit murder? Twice.'

'He just knew me, all right?'

'No, it's not fucking all right. I'd tell me if I were you. And while you're about it, I'd also tell me why the two of you murdered Miriam Fox.'

'She was blackmailing Dr Roberts,' he said eventually.

'What about?'

'He was interested in little kids.' Was. That was interesting. I'd pick him up on that later. 'She found out about it.'

'How? I'd have thought she was a little bit old for a child molester.'

'She was. But he was diddling one of her mates from the home. Her mate must have told her about it and she started putting the squeeze on. Told Dr Roberts he'd have to pay her to keep quiet.'

'So she had to die?'

He nodded, looking away. I took a drink from my beer and watched him closely.

Roberts's number must have appeared on Miriam's phone records too, but in my shock at seeing Carla's name there I'd overlooked it. Perhaps if I'd been concentrating harder I could have wrapped this whole thing up a lot sooner. And Carla would still have been alive.

'And that's it, then?'

He looked up at me, his face asking to be believed. 'That's it. That's how it was. You know, I didn't mean to get involved. I wish I hadn't. I really do. I just want to be left alone now; you know, to get on with my life.'

I sighed. 'Two people dead just because some crack-addicted street girl threatens to make accusations.'

'That's how it was,' he said, an irritatingly earnest look on his face. 'I honestly wish I'd never got involved.'

'I bet you do.' I lit another cigarette. 'That Miriam Fox must have been some blackmailer.'

'She was. She really knew how to turn the screws.'

I sighed, then walked over to Kover. I leaned down close to his face and lit the flame on the lighter. He cowered back in the seat again. 'You're lying,' I told him. 'It was more than just a case of a doctor abusing his patient, wasn't it? Tell me the truth. What was going on between you and Roberts, and why did Miriam have to die?'

I kept the flame inches from his petrol-soaked face, determined that I would get the whole truth out of him. It wasn't that his story wasn't plausible, although it still didn't explain his relationship with Roberts; it was more that he was too keen to get me to swallow it. I've seen that sort of behaviour before from criminals. They want you to believe a certain series of events, even if it incriminates them. The reason's simple: they're usually hiding something worse.