'Nothing from you. All you have to do is go back home for the night and stay there.'

'That ain't a lot. Forty quid's fuck all. I could earn ten times that.'

'It's all you're going to get. And you don't have to do anything for it.'

She thought about it for a moment. 'Make it fifty, and I'll do it.'

'You're in the wrong job. You ought to be a trained negotiator.'

I insisted on going back to Coleman House with her as I didn't trust her to go alone. We got a black cab and the driver gave me a dirty look when he saw her in tow. In the end, I felt dutybound to show him my warrant card so he'd know I wasn't some perverted punter who'd forgotten his transport for the night.

We didn't say much in the cab, and when we arrived she jumped out without a word along with her fifty quid, and disappeared inside. I could have just gone back home, but while I was there I thought I'd check to see if Carla Graham was around. Malik was right, she wasn't my type, but there was not exactly a wealth of good-looking women in my life, so I liked to make the best of any opportunities I got in that department. Even if it was just talking.

I had to ring the buzzer to get in. A woman's voice came over the intercom. She couldn't say her 'r's, and I recognized her as one of the staff members we'd interviewed yesterday. I think she'd called herself Katia, or something equally bizarre beginning with a K. A youngish girl with a revolutionary's stare who'd come across as the sort who thinks all coppers are Nazi stormtroopers just itching to truncheon a few minorities. I told her who I was and asked if it was possible to speak with Ms Graham.

'I think she's with Dr Woberts,' she told me. 'I'll just see if she can be made available.'

'Tell her I'll come back first thing tomorrow morning if it's more convenient,' I said, thinking that that would probably be less preferable to seeing me now.

About thirty seconds passed, then the door opened. 'Katia' stood there, looking overweight and tired. 'She's in her office,' she said, glaring at me as if I'd just pinched one of her nipples.

I nodded and walked past her. The place was quiet, making me wonder where everyone was. Up to no good probably. Anne would surely be out again in ten minutes, making my cash gift to her an even bigger waste of time than I'd already thought.

I knocked on the door of her office but walked in without waiting for an answer. Carla Graham was standing by her desk talking to a short middle-aged man in a three-piece suit. She was wearing a light grey trouser suit with a white blouse. A simple string of pearls adorned her neck.

She smiled at me, but I thought there was a hint of effort in it which I've learned to get used to – you have to when you're a copper – but which still disappointed me, coming from her. 'Sergeant Milne. You must be working overtime tonight.'

I smiled back, stepping up to the desk. 'Unfortunately in our job it's difficult to keep to office hours. Thanks for taking the time to see me.'

'You only just caught me. This is one of my colleagues, Dr Roberts. He's a child psychologist.'

We shook hands.

'I'm not actually based here,' he said in a pleasant, almost feminine, sing-song voice. 'I do work at sites all over the borough.'

'I expect you're kept fairly busy, then.'

'We have a lot of children with special needs, but it's very satisfying work.'

'I'm sure it is,' I said, not meaning it at all.

'I understand you're investigating a murder,' he said, looking at me with undisguised interest. He had quite a jolly face, which struck me as unusual for his line of business. Most psychologists spend their whole lives with their heads up their arses. For a profession with such a huge and constant failure rate, they take what they do remarkably seriously.

'That's right,' I said. 'A girl not much older than some of the people you deal with. Her name was Miriam Fox. She was a runaway.'

He shook his head. 'It's a tragedy, Sergeant. I always feel if we can influence them while they're young, we can help prevent them taking the path that leads to this sort of thing.'

I felt like telling him that he and his colleagues had always had ample opportunity to do just that, but had clearly failed. But I didn't. The doctor looked a sensitive sort and I didn't want to upset him. For some reason, I actually thought he seemed quite a nice bloke. He reminded me of an eccentric music teacher I'd had in school who used to wear brightly coloured bowties and who was truly enthusiastic about what he did. I'd never liked music at school, it was one of those subjects that seemed to glory in its irrelevance, but I'd always liked classes with him.

'It must be a frustrating task,' I said.

'And how is the investigation going?'

'These things take time, but we're confident of a result.'

'I understand there's been an arrest.'

I eyed him curiously. 'That's right. How did you know?'

He smiled. 'I'm addicted to the news, I'm afraid, and now I have the internet on my laptop, I'm always checking what's happening. The local news said a man surrendered himself to the police today.'

'That's correct, but I can't comment any further on it, as you can appreciate.'

'Of course, of course, I understand. Forgive my inquisitiveness, Sergeant, I just always like to know what's going on.'

'Don't we all?' I told him.

A pregnant pause followed as Roberts presumably tried to think of something else to ask, but I guess he must have realized he wasn't going to get much information out of me because he called it a day. 'Well, I mustn't hold you up. Good luck with the case.' He put out his hand and I shook it.

He said his goodbyes, excused himself, and I turned to Carla. She was looking even better than she had done yesterday and I had no choice but to try and picture her naked.

'I was just about to finish for the night, Mr Milne. It's been a very long day.'

'And I appreciate you seeing me, Ms Graham. Look, is there a pub near here? Maybe we can talk in less formal surroundings, if that would make things easier?' Christ, that came out easily.

She raised one of her eyebrows and gave me a funny look. Maybe I'd overstepped the mark, but you don't win prizes without buying tickets. 'Are you suggesting we go out for a drink?' There was enough of a hint of playfulness in her voice to tell me she wasn't offended.

I smiled. 'Well, technically, I suppose. But please don't feel it's your civic duty. We can talk here if you'd prefer.'

She sighed. 'There's a pub round the corner that's not too bad. We can talk there if you want, but I can't stay too long. I'm exhausted, and I've got another long day tomorrow.'

The pub was a two-hundred-yard walk from Coleman House, far enough away to avoid seeing any of the home's clients. It was a huge place, built on two storeys, and was clearly popular with the student crowd. Although busy, it was spacious enough to accommodate everyone amply and there were still a few tables spare.

As we walked to the bar, Carla said hello to two people she knew – both men, both younger than me – and I found myself feeling mildly jealous. I ordered a vodka orange in a superficial attempt to appear sophisticated, and a vodka tonic for her.

'I thought police officers weren't meant to drink on duty,' she said when we'd found a corner table a respectful distance from anyone else.

'Well, I'm not officially on duty.'

She raised both her eyebrows this time. 'Oh. I was under the impression you wanted to see me regarding the investigation.'

'I do. That's the reason I'm here, but what I want to talk to you about is off the record. I'm here in an unofficial capacity.'

She looked interested, and now I had a bit of a problem. If I was honest with myself, the only reason I was there was to see her; everything else was somewhat peripheral. I was concerned about what Anne had told me but I wasn't quite sure how I was going to explain that.