I found what I thought was the intruding spirit, and I started to weave a tune around it. The notes came quickly and fluently. I was expecting this thing, whatever it was, to put up more of a fight, but despite Rafi’s cursing and convulsions, the binding wasn’t too hard at all.

But as I was about to move on to the banishing, Rafi had a moment of lucidity. He stared at me with absolute terror in his eyes. ‘Fix . . .’ he whispered. ‘Please! Please don’t . . .’ In an instant he’d vanished again, going down for the third time in the lightless wells of his own hind brain. Asmodeus surfaced in his place, tenting the skin of Rafi’s face with the ridge poles of his own inhuman physiognomy, and blistering my ears with a curse from the arse-end of Tartarus.

I twigged it then, all of it. I knew what it was that was possessing Rafi, and I knew what I’d caught in the tightening coils of my tune. I was about to exorcise my best friend’s spirit from his own body, and leave the demon standing alone on the field.

I couldn’t just stop playing; that would destroy Rafi for sure. So I did the only thing I could think of, which was to change the tune into something else. I modulated key and pitch and tempo, trying to ground the binding power of the music in something else besides Rafi. And the demon, seeing what I was doing, fought back.

It was like being in a tug of war in which the rope is a frayed mains cable with a million volts flowing through it. I couldn’t stop, couldn’t let go, couldn’t let my concentration slacken for a moment. We wrestled for hours, the demon writhing inside my friend’s flesh, me hunched over the bathtub with the whistle jammed to my mouth, playing a skirling, nightmare arabesque.

And I won. Kind of. I bound the demon.

Only I bound it to Rafi, and I couldn’t untie them again.

It was the opposite of an exorcism: the man and the monster were welded so tightly and inextricably that they’d almost become one being. It wasn’t exactly a Jekyll and Hyde deal, though; it was worse than that. Asmodeus was calling the shots from day one. Rafi’s personality remained totally submerged, except when I was able to bring it to the surface again with another summoning.

And Rafi’s body was locked up in a silver-lined cell at the Charles Stanger Care Home in Muswell Hill, silver being a good specific against demons as well as the undead. The official diagnosis was schizophrenia, but the Stanger knew what they were dealing with and took no chances. They kept the demon down with wards and charms and neuroleptic drugs, administered in industrial quantities.