Leah is speaking again, but I can no longer see her, as the man with the knife is in the way. 'Tyler, if this is a game, stop it now. Please. You're scaring the shit out of me.'

I know the guy isn't me – I would never do anything like this – but I have an extremely serious problem. He is roughly my height and build, and given the poor quality of the recording, it's not that easy to tell one way or another. So a court of law might see things differently. Especially with the way Leah is talking. Either she's a damn fine actress or she genuinely believes it's me standing there behind the mask. And I don't think you can act as fearful as she's sounding. Her fear comes right from her bones, and it is easy to see why.

The man pretending to be me slowly advances round the front of the bed towards her side, taking his time and enjoying each step, lifting the knife higher so that Leah can see it more easily. The blade glints threateningly in the lamplight as he raises it above his head. Beyond him, I can see her struggling vainly on the bed, but the knots that bind her hold easily. She's helpless.

And then, as the guy turns his back to the camera, the trouble I'm in increases tenfold. You see, there's one way to tell without any doubt whatsoever whether or not the man with the knife, the one Leah is calling Tyler, is me. Ten years ago, I suffered a number of shrapnel injuries in a bomb attack, and I still carry the scars. Most are deep but small puncture marks, but three are noticeable from a distance. They are all on my upper back. One is like a pink birthmark, about three inches across, near the right shoulder blade. The other two are deep, thick lacerations that run down either side of my spine, almost symmetrically. The man with the knife has those three scars. They aren't that clear in the film, but if you know what you're looking for, you'll see them. And I know. I stare at them grimly, my teeth clenched tight. They are in the right place on his back, there's no doubt about that. The man in the shot may not be me, but the way things are looking, I could well end up in a minority of one holding that opinion.