Frobisher House is the second of a row of five low-rise blocks of cheaply designed 1970s flats that share an award-winning blandness, and which take up one side of the street, looking like unwelcome invaders when compared to the pretty terrace of Edwardian cottages opposite. A group of kids are playing football in the car park that runs along the front of the flats as Lucas and I pull up half an hour after setting out. If anything, the day is getting hotter as it moves inexorably towards evening.

We get out of the car and walk up to the front entrance of Frobisher House.

‘I’ll tell you something,’ says Lucas as we open the scratched and ancient Perspex doors, ‘if I lived in a dump like this, I reckon I’d resort to blackmail.’

I know what he means. There’s fresh, illegible graffiti on the adjoining wall, and as we step inside we’re assailed by a stale smell of feet and sweat which reminds me of a schoolboys’ changing room.

‘I heard he was a gambler,’ I say. ‘I guess he just wasn’t a very good one.’

Ferrie’s place is on the second floor, at the end of a corridor that smells vaguely of bleach, which is a far more tolerable odour than the one lingering at ground level. I can hear a woman shouting at her kids in one of the flats and a baby is crying irritably in another, but the corridor itself is empty. The front door to his flat is made of plywood, in keeping with the general cheapness of the rest of the building, and there are two locks on it, a Yale and a Chubb, the latter having been added recently.

‘You know,’ says Lucas, pulling a set of skeleton keys from his pocket, ‘if I had something valuable, worth all that money to someone else, there’s no way I’d hide it in here. It’s not exactly secure.’ Wanting to prove his point, he gets to work on the locks, telling me to act natural. ‘If anyone asks what we’re doing, we’re cops, OK? I’ve got some ID I can show them if they get too nosy.’

Lucas, it seems, has some fairly eye-opening working practices, and if ever the private detective work dries up, he’s definitely got a career alternative as a burglar. It takes him about a minute to pick the Chubb and half that time to do the Yale. I have to admit I’m impressed as the door opens and I follow him inside.

It leads directly into a poky little box-like living room that’s most definitely been lived in. It’s at the opposite end of the bachelor pad spectrum from Lucas’s. A threadbare sofa and a couple of armchairs that don’t match it are arranged in a very tight semicircle around a portable TV, which sits on a cornflakes box. There’s an overflowing pub ashtray on the sofa’s arm and another one on the floor, as well as various bits of used crockery that haven’t quite made it back to the kitchen. Bookshelves, groaning under the weight of piles of paperbacks, line two of the walls, and a framed poster showing an exotic beach scene, complete with turquoise sea and hanging coconut palms, takes up most of one of the others. It’s entitled ‘Paradise’, which I’m guessing is where Iain Ferrie was planning on heading if he hadn’t been so rudely interrupted. As if to prove the point, there’s a battered Samsonite suitcase next to the front door with a passport and an airline ticket balanced on top.

So Ferrie had been telling me the truth about getting out of the country fast, and given the trouble he was getting himself in, who could blame him?

Lucas puts on some plastic evidence gloves and hands a pair to me. He picks up the passport and opens it at the photo. ‘It’s him, all right,’ he says. ‘So at least we’re in the right place. Let’s see where he was going.’ He inspects the airline ticket. ‘Caracas, one way. Very nice. The sort of place I’d head to if I was a fugitive.’

He puts the ticket and passport in the inside pocket of his suit and walks across the living room and into a tiny hallway, which has three doors leading off it – presumably the bedroom, bathroom and kitchen. They’re all closed and Lucas has a quick check behind each of them before coming back into the living room.

‘There’s no laptop or computer in here,’ he says.

‘What about in his suitcase?’

He steps over, presses the handles, and it falls open, revealing a load of clothes, some shoes and a few more books, but no laptop. He shuts it again and stands back up, taking the time to look round the room with an expression of distaste etched firmly on his features, like he’s just stepped in dog mess.

‘OK,’ he says at last, ‘the sooner we start, the sooner we finish. Rules are these: we try to be as quiet as possible but we turn over everything. And I mean everything, including the carpets. He was a blackmailer, so he wouldn’t just leave stuff lying around. If you find anything with his handwriting on, however innocuous it looks, put it to one side so we can check it later, because he might be writing stuff down in code. And keep a real eye out for electrical devices. Blank CDs, flash drives, anything he might have stored information on. And definitely mobile phones. I’ll start in here. You take the bedroom. Let’s go.’

Ferrie’s bedroom is less cluttered than his living room. There’s a double bed with matching bedside tables on either side, another bookshelf full of books, and a built-in wardrobe. The doors to the wardrobe are open and I can see that most of the clothes have been removed, although there are still a couple of winter coats hanging up among the empty coat hangers.

There’s a six-by-four photograph in a garish silver frame of Ferrie and his bride on their wedding day on top of one of the bedside tables, and before I start I pick it up. In the picture, a younger-looking Ferrie wears a morning suit dotted with confetti, and a purple cravat. Standing next to him, her head almost touching his, is a pretty, wholesome-looking blonde woman of about the same age in a wedding dress. They’re both smiling at the camera, although her smile is wider and looks more genuine than his.

Looking at the photo now, I find myself feeling sorry for him. I know he brought his demise entirely upon himself, but it’s still hard to see a picture of someone smiling on what I’m assuming was one of the happier days of his life, knowing that his life was snuffed out violently only hours earlier. It’s an unwelcome reminder of my own mortality. The same bullets that killed him were also meant for me, and it’s only through a combination of luck and training that I’m still standing. Nor is it over yet. There might come a time, and it could potentially be only hours away, when a world-weary detective stands in a bedroom not so different from this one, gazing at the old wedding photos I still keep in one of my drawers, wondering whether the man whose death he’s investigating deserved his fate.

It’s an unpleasant thought, and I swiftly shut my mind to it as I put down the photo and get to work, moving methodically through the room from right to left, occasionally stopping to wipe sweat from my brow. It’s hot in here, and with the window closed the air’s stagnant. I hear a lot of shouting coming from next door, and although there’s a dividing wall separating us, I can hear every word. A teenage boy is having an argument with his mother. He swears a lot and is so disrespectful to her that if I wasn’t stuck in here with my own problems I’d go round and clip the little bastard round the ear. His yelling reaches a spoilt, inarticulate peak, then a door slams and I’m left once again in heavy, humid silence.

I take the books from the shelves one by one and give them a quick flick through to check if there are any loose slips of paper inside, before discarding them on the floor. I find myself interested in Ferrie’s reading habits. He likes crime fiction, and he’s got quite a few old classics – Raymond Chandler and Mickey Spillane from the States, as well as a whole heap of Agatha Christies. He’s got some contemporary stuff as well by a bunch of writers I’ve never heard of, but then I don’t read so much myself these days, and when I do, it’s usually biographies.

It’s no fun searching the home of a dead man, but at least you don’t have to worry too much about being tidy. Having found nothing of use among the books, I tear up the carpet (nothing under there either) before stripping the bed of its sheets and turning it on its side. But, as that too turns up a blank, I’m beginning to doubt we’re going to find anything of use. Ferrie was planning on leaving the country as soon as he got his money, so there was no reason to leave any kind of clue behind. ‘Something you don’t ever want to see’ were his words to describe the briefcase’s contents. If it was truly something that bad, surely he would want no evidence of what he was involved in to remain in circulation.

But the guy with the pistachios back at the brothel hadn’t been convinced. He’d wanted Ferrie’s real name, even when he knew he was already dead, and the only possible reason for that is that the people he was blackmailing believed he might be holding something back. So I keep beavering away, conscious that with each passing minute the trail is going that little bit colder, and bringing us closer to the time when Lucas will be questioned by the police about Snowy’s murder. And then they will be after me too.

To be honest, this particular thought’s really beginning to play on my mind, so it hardly registers when my fingers find something in the pocket of one of Ferrie’s winter jackets. But when I pull out a little black book with a single word embossed in gold on the front, it makes me want to praise the Lord aloud. It says, simply, ‘Addresses’.

I leaf through it quickly. There are scores of names in here. I don’t recognize any of them, but why should I? I never really knew the guy, and he never really knew me. Just to confirm this, I check whether my own address is there. It isn’t, but Lucas’s is. His office one, anyway.

Then I have an idea. I check under M, but the name I’m looking for isn’t there, so I start again from the beginning of the book, reading the names of the contacts one by one. An old army name pops up in the ‘E’ section, Neil Ellison. I remember him vaguely. He left years back and I haven’t seen him since. ‘F’ comes and goes with a few family members; ‘G’ and ‘H’ have only one name apiece, which makes me think Ferrie wasn’t one of the world’s more popular guys; and then in ‘I’ I finally find what I’m looking for. In the brothel, the blonde woman who incapacitated me with the stun baton before intervening when I was about to get shot, referred to the big guy, Rubberface, as Marco. Staring up at me from the page is the name Marco Itinic, and beneath it a London address in the postal district of W2. I think about carrying on through the rest of the address book, but I know that someone like Ferrie is not going to know two men called Marco.

I can’t hear much in the way of activity next door in the living room so, thinking that perhaps I should be retraining as a PI since I’ve obviously got the knack for it, I stride through to show Lucas what I’ve found.

But as soon as I get inside the living room I stop. It looks like Lucas has found something too. It’s in his hand, and he’s inspecting it carefully with a shocked expression on his face.

For a moment, he doesn’t acknowledge my presence, so lost in thought is he; then, slowly, he looks my way, and as he does so he lifts the object up between his thumb and forefinger so that I can see it clearly.

At first I can’t work out what it is, but when I step forward to take a better look, I recognize it instantly. I’ve seen such things before, spilling out of the muddy earth in the genocidal killing grounds of Kosovo and Sierra Leone like grisly offerings. Yet still I hear myself taking a sharp intake of breath.

Because what Lucas is holding, stained and dark with decay underneath the thick seal of clingfilm wrapping, and with the first, jaundiced glint of bone showing through, is a human finger.