They made the first tentative steps towards creating their own infrastructure – zombies in particular have some very specialised needs – and predictably the living responded by dividing into antagonistic camps, the Breath of Life movement calling for a recognition of dead rights, while groups like the Catholic Anathemata preached the imminent apocalypse and started stockpiling weapons for it. Meanwhile people in the ghost-busting trade started to talk about encountering other kinds of creatures that had never been either human or, strictly speaking, alive: creatures that seemed to fit the mugshots of the demons described in medieval grimoires. I even met a few myself – encounters that I still relive in dreams, and probably always will.

Two thingsay m"">Two eventually had to happen before I started to realise that tooting my whistle first and asking questions later was a flawed strategy. The first was me fucking up someone else’s life beyond all possible unfucking, and the second was having my own life saved and handed back to me by a dead woman I was trying to exorcise. These days I don’t do straight ghostbusting any more: if you look at the sign over my office door, you’ll see that it says I provide SPIRITUAL SERVICES. No, I don’t know what that means either, and it doesn’t do a hell of a lot to bring in the passing trade. But that suits me okay, in a lot of ways: the closest thing I’ve got to a philosophy is that I’ll do anything for a quiet life except work for it.

So what kind of a spiritual service was my old acquaintance John Gittings in need of? As I sidestepped out of the way of a broken-off chair leg that left a dent in the wall at the height of my crotch, I ran through some of the options – from the humane to the extreme. None of them looked good right then except slamming the door shut behind me and making a run for it.

Geist! It was like finding out that your best friend is a cannibal after he’s just offered you a chicken sandwich.

Well, maybe not quite like that: John had never been a friend, exactly. Including one memorable skirmish with a werewolf at Whipsnade Zoo, in which he’d modified our sketchy battle plan on the fly and almost gotten me eaten alive, I’d seen him maybe five times in the last three years.

It was still a shock, though, and I was having a hard time getting my head around it. Like I said, most ghosts are passive and harmless: it’s only the most disturbed souls who go geist after death, their tortured personalities subliming through some terrible metamorphosis into an unliving storm of anger and frustration.

But John Gittings? In the words of Denis Healey, it was like being savaged by a dead sheep.

I turned to Carla, realising what she’d been going through; why she’d asked me to come home with her, and what she’d tried and failed to say as we were driving back here.

I put a hand on her arm and gave her a firm push towards the door, seeing in her eyes that she was about to start crying again, and afraid that this time she might not be able to stop.

‘Wait in the car,’ I said.

She stared up at me, frightened and hopeful in about equal amounts – and some of what she was scared of was the same as what she was hoping for. ‘What are you going to do?’ she demanded.

‘What you asked me to do. Give him some peace.’

‘You won’t-?’

‘Exorcise him? Send him away for ever? No, Carla. I won’t. I promise. Wait in the car. It shouldn’t take longer than twenty minutes.’

She took one last look past me into the room, where an invisible entity was trailing some extension of itself through the broken glass on the carpet, making it bristle and shift. Then she nodded and backed out through the door, staring all the time, as if turning her back would have felt like a betrayal. I closed the door gently behind her, then knelt down and unshipped my whistle.

I keep it in a pocket I’d sewn into my coat myself, high up on the left-hand side. A paletot is handy like that – it’s so voluminous that you can carry a drawerful of cutlery, a samovar and a sub-machine gun around with you and it won’t even spoil the line. I generally just keep the whistle, a silver dagger, an antique goblet I’ve never yet had occh tr yet hasion to use and a bottle of whatever booze I’m currently flirting with.

I blew a random sequence of notes to tune it in – except that even then, even on this first approach, it wasn’t quite random. There was an element of echolocation in it: of throwing out sounds to see how they’d come back to me again – to see which the ghost absorbed and which bounced off and rolled away into the ether. These are just metaphors, you understand: but everything I do is a kind of metaphor. You choose the tools that work, or maybe they choose you."

"And sometimes it comes hard and slow, sometimes quick and easy.