'Detective Sergeant Milne. I'm sorry, sir. I didn't realize.'

I shrugged my shoulders. 'Course you didn't. You're just doing your job. But if you don't mind, I'm in a bit of a hurry.'

'Of course, sir, no problem.' He stepped back from the car. 'Have a nice evening.'

I said goodnight, and put the car in reverse. Poor sod. I remembered only too well what it was like to be out on nights like these, being paid a pittance to stand around for hours on end with the rain pissing down on your head. Knowing that the people you were meant to be looking for were probably miles away. Oh, the joys of being a uniformed copper.

I waved as I drove past, and he waved back. I wondered how long it would take him to lose the enthusiasm; how long before he, too, realized that by playing by the rules he was just banging his head against a brick wall.

I gave him two years.

I used to know a guy called Tom Darke. Tomboy, as he was known, was a buyer and seller of stolen goods. If you'd nicked something – whatever it was – Tomboy would give you a price for it, and you could be sure that somewhere down the line he'd have a customer who'd take it off him. He was also an informant, and a good one too if you measure such things by how many people his information convicted. The secret of his success lay in the fact that he was a likeable character who was good company. He used to say that he listened well rather than listened hard, and he never asked too many questions. Consequently, there wasn't a lot that went on among the North London criminal fraternity that he didn't know about, and such was his affability that even as the local lowlifes were going down like overweight skydivers no-one ever suspected old Tomboy of being involved.

I once asked him why he did it. Why, as the Aussies would say, did he dob in blokes who were meant to be his mates? Because the thing was, he didn't really strike me as the grassing sort. He came across as being a decent bloke who was above such petty deceptions. Tomboy had two answers to this question.

The first answer was the obvious one. Money. There were good rewards on offer for information on criminals and Tomboy needed the cash. He wanted to retire from the game with his freedom intact because he believed that with the onset of technology, and its availability to the police for fighting crime, the writing was on the wall for middle-ranking career criminals such as himself. So it was a case of making hay while the sun shone, building up a nice little nest egg (he'd set a target limit of £50,000), and then getting the fuck out.

The second answer was that if he didn't dob them in, someone else would do it anyway. Criminals are usually notorious braggarts. Since they can't tell the whole world what they've done for fear of retribution, they like to boast about their exploits to one another. And since by definition they're a dishonest lot – as Tomboy once said, 'Whoever heard of such a thing as honour among thieves?' – sooner or later someone's going to inform on them if the money's right. All he did, if you believed his rationale, was get in there first.

So that was Tomboy's philosophy. There's no point in not doing the deed because one way or another it's going to get done, and if you're going to get paid to do it, all the better. I thought about that as I drove home through the rain that night. If I hadn't killed those men, someone else would have shot them. Either way they ended up dead. If you're in the line of business where you make enemies of people who'll pay to have you killed, you've got to be prepared to accept the consequences. That was how I justified it to myself, and that was how Tomboy had always justified it to me, and it had never done him any harm. In fact, it appeared to have done him a lot of good. The last I'd heard he was living out in the Philippines. He'd made his fifty grand, probably a lot more knowing him, and had invested it in a beach bar and guesthouse on one of the more far-flung islands. He'd sent me a postcard from there a couple of years back on which he'd extolled the virtues of the laid-back tropical lifestyle. It had ended with him saying that if ever I fancied a job working at his place, I should let him know.

More than once I'd felt like taking him up on the offer.

It was getting close to eleven o'clock when I got home that night, home being a rented one-bedroom flat at the southern end of Islington, not too far from City Road. The first thing I did was take a long hot shower to wash the cold out of my bones, before pouring myself a decent-sized glass of red wine and settling down on the lounge sofa.

I turned on the TV and lit a cigarette, relaxing properly for the first time that day. I took a long slow drag, enjoying the fact that a potentially hazardous job had been completed successfully, and flicked through the channels until I found a report on the killings. It didn't take long. Murder's a numbers game. Kill one person and you barely make the inside pages. Kill three, especially in a public place, and it's big news. It adds a bit of excitement to the mundane grind of people's lives; even more so when it bears all the hallmarks of a so-called gangland shooting. Shootings are entertaining because they're not too personal. They make good conversation points.

Understandably, details were still very sketchy. The programme I was watching had a young female reporter on the scene. She looked cold but excited to be involved in what was potentially a meaty, career-enhancing story. It was still raining, only now it had turned into that light stuff that always seems to soak you more. She'd positioned herself in the rear car park and you could make out the Cherokee in the background about twenty yards away, behind reams of brightly coloured scene-of-crime tape. There were a lot of police and forensic staff in lab coats swarming all over it.

The report didn't last long. The girl confirmed that three people had been murdered – no idea as to identities – and speculated that they'd been shot. She then wheeled over the hotel's deputy manager, a tall, spotty young man who looked like he'd just got out of school, for his comments. They weren't, it has to be said, very enlightening. Squinting through his spectacles, he explained that he'd been working in the reception area when he'd heard a number of faint popping sounds (they all say that) coming from the rear car park. He'd thought nothing more of it but then one of the kitchen workers had come running in screaming and shouting that there'd been a murder. He, the deputy manager, had bravely gone out to investigate and had immediately discovered my handiwork, which was when he'd called the police. 'It was very shocking for all of us,' he told the reporter. 'You don't expect this sort of thing in a quiet area like this.' They all seem to say that as well.

The reporter thanked him before turning back to the camera and breathlessly promising further information as and when she received it. She then signed off, and it was back to the studio. It seemed I'd made her night anyway.

I took a drink of wine, taking my time swallowing it, and switched over. There was a programme about great white sharks on the Discovery Channel, and I sat watching that for a while, not really paying too much attention. Although I tried to empty my mind of the day's events, it was difficult not to think about the murders. I suppose it was only now that the full enormity of what I'd done was beginning to sink in. Three lives snuffed out, just like that. It felt like I'd crossed a threshold. I've killed before, I suppose that's obvious by now, but only twice, and in vastly different circumstances.

The first time was twelve years ago. I'd been one of a number of armed officers who'd turned up to a domestic incident at a house in Haringey. A man was threatening his common-law wife and their two young children with a gun and a carving knife. They'd got people trying to negotiate with him over the phone but the guy was drugged up to the eyeballs, shouting incoherently, and they weren't really getting anywhere.