Will Self: PsychoGeography

Glencoe. It's late August but already there's a hint of autumn in the air, along with the droplets of smirr and the midges dancing between them. Further south the heather is still in full flower, but up here in the central Highlands, the stark triangles of the mountains are at first tawny, then swathed in grey mist, then tawny again. I unload the car and pitch the tent, while the small boys head off to explore the riverbank. I want them to fetch firewood, but they return empty-handed: over the summer the campsite has been picked clean; bucolic louts have even hacked at the living alders and birches.

I head off downstream to where some large timber has been disgorged on to the stony bluffs. It's too large: entire trees, their root systems embedded with rocks lie like stranded krakens. I wrench a couple of limbs off and drag them back, then gather a few handfuls of twigs and wager our last firelighters on stimulating a conflagration. Dusk and clouds are flowing down into the U-shaped glacial valley, the midges are getting fierce: We need smoke.

Then comes Colin. I've encountered him already, a portly, middle-aged man, in grey tracksuit bottoms and a check wool shirt. He has a regulation bald patch, and as I passed him on the path he wished me a cheery "Good evening" in a New World accent that I couldn't place. Now he comes up to our fireplace and says, "I heard the kids' voices and had to come over, I'm missing my own ones and dying for a little company," then he giggles, a disagreeable cartoon chuckle. "I was sitting at home in Glasgow at six this morning, when I decided that I couldn't stand the city anymore, so I got in the car and drove up here," again the naughty giggle and a conspiratorial look. I came here to get away from all Colins, but this one has latched on effortlessly.

"I don't think that's gonna catch," he says, gesturing at the fire. It's true. The early promise of the firelighters has given way to a forlorn charring. "I've got some kindling and logs in the car, if your lad'll give me a hand," he gestures at my 9-year-old, selecting his volunteer, "I'll go and get them."

"Go on then, Ivan," I say, but as he obediently trots off through the woodland behind Colin I am gripped by a dreadful anxiety: this Colin isn't just some saddo loner with grating mannerisms, he's a highly organised paedophile, who's going to whip my son into the back of his car and drive him away ... Glencoe will become the ominous backdrop for another bloody massacre ... Then I check myself: Christ! I'm falling victim to just the free-ranging, stranger-danger paranoia I so despise in the commonality; I'm damning a man for a pervert simply because he's being friendly. I hunker down to the fire, trying to coax it back into life – but it's no good, the anxious worm is boring through me, and I find myself scampering through the woodland in studiedly casual pursuit, only to encounter Colin and Ivan on their way back with the logs.

So, having falsely accused him, I'm condemned to Colin for the evening. Still suspicious I draw him out. It's a rule of meetings with unremarkable men, that if you question them, they'll remain transfixed by their own incuriosity. So it is with Colin. While we get the fire going (and even with his logs, his coal and his kindling, it fails to properly ignite until he applies his electric air pump), and the boys toast their marshmallows and slurp their hot chocolate, I learn a lot about him, while he remains in total ignorance of us.

Colin's parents emigrated to Canada when he was a kid. He grew up there, joined the Canadian Navy, trained as a radar plotter, then left and came back to his native Scotland in the early 1990s. He hasn't worked properly since. He has a girlfriend and a couple of kids. He's also got diabetes and has had five heart attacks. I'm shocked when he tells me he's four years younger than me – he looks much older. He sits at home in Glasgow, growing hydroponic weed in his cupboard, which explains the giggling and the claustrophobia. Every so often he drives his Mondeo up north and squats in this campsite, staring out at the mountains he's incapable of climbing.

As I pump Colin for his life story a sadness emerges that blankets Glencoe as thickly as the darkness. Even when he gets out the 12 million candle-power torch he bought at Argos for £29.99 it fails to dispel my gloom: this is just a cock-up of a man, no conspirator. Eventually, the small boys are asleep on their rug by the fire, and Colin takes his leave: "I've got my laptop in the tent," he tells me proudly. "I'm gonna watch The Da Vinci Code."