He nodded. 'Yeah, she did. And I tell you something, it took a fuck of a lot of phoning round to find out. The company's going to send us a list of calls she made and received over the past month.'

'Maybe it'll throw up something.'

'You never know,' he said, but he didn't sound that interested. In his mind, we'd already got our man.

As predicted, we ended up spending several hours at the children's home that afternoon trying to track down the various 'clients' we hadn't yet spoken to. We managed to pin down a few but no-one who could help us much. To be honest, it did prove to be a bit of a waste of time. Carla wasn't there either, which disappointed me. She had a meeting out in Essex and hadn't returned by five o'clock, which was the time we'd decided that we'd had enough. I phoned through to Welland and told him that he might as well send uniforms down for the rest of the statements because it simply wasn't worth using us for it, and he agreed without much resistance.

That evening it was Malik's turn to take off early. He had to pick his kids up from his mother-in-law's as his missus, who was some high-flying accountant, was off on a seminar in Monte Carlo or some other such exotic destination. It made me think. The last seminar I'd attended had been in Swindon. 'The Role of the Police Force in 21st-century Britain ' it had been called – about as interesting and informative as watching a car rust. I was definitely in the wrong job.

We left together and I took the tube down to King's Cross. I thought about heading back to the station and seeing what needed doing but decided a drink might be better instead. Welland had told me they were still questioning the pimp, and so far there was nothing of note to report, which didn't surprise me. You only turn up with your lawyer in tow if you don't want to say too much.

I found a pub on the Euston Road near the station which didn't look too shitty and took a seat at the bar. The barman was a young Australian guy with a ponytail and a silver ring through his eyebrow. There were only a few people in the place so we had a bit of a chat about this and that. He was a friendly sort, which is often the way with Aussies. I think it must be something to do with the fact that they're brought up in a nice sunny climate. I asked him what the crime situation was like over there. He told me it was pretty bad.

'It's getting worse too, y'know,' he said. 'A lot of guns around the place, and people more willing to use them.' I told him that that was the case everywhere. 'Don't I know it,' he said. 'Especially here. I always thought London was supposed to be a safe place.'

'I think you're about fifty years too late,' I told him, and we left it at that.

When I left the pub, shortly after seven o'clock, I decided to walk home and take in some of the sights of the red light district where Miriam Fox and her young friend, Molly Hagger, had plied their trade.

King's Cross isn't a lot like people expect a red light district to be. On the main drag there are the two railway stations on one side of the road, almost next to each other – King's Cross and St Pancras – while a few dodgy-looking fast-food outlets and amusement arcades cluster together on the other. A couple of ageing sex shops with their trademark blackened windows and garish lighting are the only sign that people come to the area with sex in mind, but even they look lonely and a little out of place. King's Cross is no Amsterdam or Hamburg. There's no obvious prostitution activity on the main roads, even after dark. The prostitutes might be there, but you wouldn't particularly notice them. The area tends to be fairly busy as the Euston Road links the west and east of the city, and there are always plenty of people about, which deprives the punters of their one great desire: anonymity.

But step away from the bright lights and into the dark, dimly lit backstreets and a new world awaits. Drifting in and out of view like ghosts are the whores and the crack dealers. Sometimes you don't even see them. Their disembodied voices reach out from the doorways and alleys and the questions they ask are always the same: 'Need any gear?' 'Looking for a good time?' Sometimes you can feel their eyes boring into you, trying to work you out, looking for your weaknesses, maybe deciding whether or not you're worth robbing. Cars ease idly by, sizing up the scene. If you look at them, you'll see that most of the time the occupant is a single, middle-aged man and they never return the look. They always turn away. These are the businessmen searching for their illicit thrill. Some of them are just frustrated, and need a quick fuck to bring them fleeting satisfaction. Others are perverts, people who want to do things to a woman their wives and girlfriends would never countenance. People who want things done to them that you and I couldn't countenance. And somewhere among them are the psychopaths, rapists and killers sweeping the area in their constant hunt for prey. This other world exists fifty yards from King's Cross station, but unless you look for it you'll never see it, and unless you see it you'll never understand the sickness that keeps it going.

It was a mild night with a strong wind. In my raincoat pocket I clutched a small cosh I occasionally carry about with me, purely for emergencies. It's less than a foot long and easily concealable on a winter's day. I've never used it in anger before and I'd never think about wielding it while on duty – it's more than my job's worth – but I was glad I had it now.

Two ageing prostitutes, their faces cracked and wrinkled like old leather, stepped out of the darkness and into my path. They wore ridiculously short skirts and pantomime make-up. 'How about some, love?' said one, forcing a leering smile. 'With a real woman.'

'I'm a police officer,' I said, pushing past her as politely as possible.

'So? Even coppers need a bit of fun,' she shouted after me. But her enthusiasm had faltered.

I didn't say anything. What was there to say to that?

I felt sorry for her. I felt sorry for them both. According to some of the other guys on the case these older girls were bitter about the competition provided by their more youthful counterparts like Miriam Fox and her friends, which was no great surprise. It's difficult enough to compete with newer, better, different models, and even worse when they undercut you. This rivalry had resulted in a number of incidents where older prostitutes had attacked the young ones, and several where they'd actually called the police to tell them about underage activity in an effort to get the girls off the street. Now the two competing groups tended to keep apart, but it was youth that had the most success.

It was quiet tonight, a result no doubt of the investigation, but business would soon return to normal. In the end, nothing gets in the way of capitalism. That's what's always annoyed me about the British attitude to paying for sex. It's all well and good having a big moral stance against prostitution, but that doesn't stop it happening. It doesn't even curtail it. Far better just to regulate the trade so that the girls are clean, pimp-free and safe, and the red light districts become tourist attractions, not drug-infested no-go areas like the one I was walking through now. Girls like Miriam Fox would almost certainly still be alive if they'd worked in Amsterdam or Barcelona, or wherever they were sensible enough not to attempt to change the laws of nature.

The scream came from somewhere behind me.

I didn't even register it the first time. You expect a scream on a street like this. Then it came again, louder and more desperate. It sounded like a young girl – a teenager – but whoever it was was pleading for help, the voice growing increasingly hysterical, and I knew straight away that something was badly wrong.