First of all, it wasn't trick photography. It had been through every AV specialist unit in the country, passed every test, been torn apart frame by frame, but even with all that gadgetry thrown at it, it kept coming up clean over and over again. Whoever had cooked up this little bit of chicanery hadn't used trick photography: something had definitely been on the island beach that hot 18 July two years ago.

That morning I played it again on my laptop. I sat forward on the edge of my seat, concentrating hard. I'd seen it a thousand times and knew every frame. It started off kind of ordinary, with the camera lingering on the horizon out to sea, tilting gently as the single-engined boat bobbed on the waves in the Firth of Lorn. I dragged the RealPlayer toggle to the bit where a shout went up on the boat. This was the exact moment when one of the other tourists saw something moving on the island. A few indistinct shouts came from the TV — a lot of camera movement as the surprised tourist whipped the videocam sideways, taking in one or two shocked faces on the boat, then focused across the bay on an indeterminate line of green-brown — the seaward shoreline of Pig Island. Someone close to the camera spoke. The words were totally unintelligible because of the wind on the soundtrack, but the BBC unit had added sub-titled dialogue to my copy: 'What in fuck's name is that?'

This was the important bit. You could feel the guys on the boat inching forward in curiosity, staring at the beach where a creature no one could put a name to moved ponderously through the foliage at the water's edge. It stood at about five foot eleven; the BBC technicians figured this out from comparative measurements using sun and trees. In most ways it appeared like a naked human being — the video showed its back from the waist down; the upper half was concealed in shadow. Except it wasn't human. There was something dangling from the base of its spine. Estimated to be about two feet in length, the same battered brown flesh as the body, it looked just like a fleshy tail. It banged once on the back of the creature's legs as it moved.