A moment that changed me: I saw a big cat on Dartmoor – and no one believed me

I was 11, with a handful of friends on a school trip to Dartmoor. We’d set up our tents near the edge of a camp, which was mostly empty.

The first morning, our tent woke before the teachers. We stole out to find another group of boys already on the dewy grass, standing hands in pockets, together in nature. The sun was just coming up. The last of the night-time mist was peeling away.

We were making jokes in the way boys that age do when trying to stay silent – pulling exaggerated faces, making rude gestures – when someone pointed. There in the distance, perhaps 15 metres (50ft) away, stalking just beyond the wire fence, was a dark shape in the fog. It moved closer, from right to left across our field of vision – the unmistakable shape of a big cat. Much, much bigger than a house cat, more the size of a large dog. Bigger, even.

‘As a child, you take an adult’s words as gospel’ … Lury at 13. Photograph: Courtesy of Max Lury

There is a distinctive, swaggering weight to the movement of a cat that size. The shoulders roll. The head is squarer, the tail longer and thicker than a house cat’s, with a distinctive slope. We stood there, transfixed, in total silence. I can remember its dark fur silhouetted against the thin white mist behind. The animal didn’t seem in a rush to leave. We were so shocked that we didn’t know how to feel. Half scared, half in disbelief. Fascinated. None of us had heard of anything like this before.

Eventually, one of the boys ran into the tent to grab a camera, but by the time he returned, the animal had stalked off.

When we told our teachers what we had seen, they assumed we were making it up. They thought we were pulling a prank and somehow making fun of them. Their responses went from frustrated to angry to tired. By the end of the weekend, most of the other boys who had seen the big cat had been convinced by the teachers’ arguments.

But there was something about that morning that I couldn’t shake. On the one hand, there was the experience of seeing something that should be impossible right in front of you. It felt like peering through a portal into another world. On the other, there was the feeling of being told by adults that what we had seen wasn’t true. At that age, you take an adult’s words as gospel: they know things, you don’t. But I knew I had seen a big cat – and each time I was told I hadn’t, the certainty inside me grew.

This conviction turned into an obsession. That year, I spent lunchtimes in the school library searching for answers. It turned out that there were hundreds of accounts of sightings of big cats on the moors. The accepted wisdom is that big cats – pumas, cougars, even panthers – may have been released on to the moors after the Dangerous Wild Animals Act became law in 1976. Perhaps, some think, people buy big cats illegally as exotic pets, then release them into the wild when they become unmanageably large. However, there is no concrete evidence of big cats’ existence on the moors and scientists maintain that a breeding-size population is all but impossible.

Dartmoor at dawn … Bellever Tor. Photograph: Mark George/Getty Images

I soon began reading everything I could about “cryptids”, creatures whose existence is disputed or unsubstantiated by science. I devoured the stories: a lingering population of thylacines, or Tasmanian tigers; sightings of Mokele-mbembe – a mythical water-dwelling entity – in the Congo basin; static-flecked audio recordings of Bigfoot screams in the US. Each time I came across something difficult to believe, that initial moment of resistance – the speck of doubt – was overridden. I could understand the real, human feeling behind the story. I could open myself up to believing.

Of course, there are often reasonable explanations, too. Memory can play tricks. The size of certain animals can be difficult to guess. Some house cats grow to be unusually large. Sightings of Mothman (a winged cryptid associated with Point Pleasant, West Virginia) are often attributed to people being unable to comprehend the size of owls at night. With their 1.2-metre wingspan and huge eyes, turned to a single plate of colour in torchlight, seeing one swoop towards you in the dark can feel as if you’re looking at something demonic.

These days, I don’t believe everything I read about the supernatural. But when a friend, or a stranger at a party, tells me about a ghost they’ve seen, or a room that seemed to be filled with a sinister energy, I leave a little more space for it. I let myself – even if just for a moment – believe.

• No Ghosts by Max Lury is published by Peninsula Press on 16 April (price £12.99). To support the Guardian, order your copy at guardianbookshop.com. Delivery charges may apply