Five-minute memoir: A chance encounter breaks Elanor Dymott's seaside solitude

In Cornwall, the end of September, walking the coast to St Ives. A slight chill in the air but the sun still warm on my face. I've booked a night at Gurnard's Head and then, tomorrow evening, return to London.

Zennor village is not far off now; a quiet stretch in any season. I wanted to be on my own and it's worked. The path has been mine for the past five days and I'm assuming things will stay that way. So when I see him ahead I'm surprised and half-hang-back, easing my pace and hoping he'll speed up and vanish. Instead he slows down, glances in my direction once or twice. When he comes to a halt altogether I consider changing course but decide against it, resolving to say a quick "Good afternoon" and keep myself to myself.

We draw level at Porthmeor Cove. His opening gambits are reasonable enough: he made a pre-dawn start from Land's End and wants to reach the inn at Gurnard's Head by suppertime; he's worried he might have missed the turning; his iPhone's dead and he's forgotten the map for that part of the route, so could he look at mine?

"You're nearly there," I reply. "Half an hour-ish, you'll see the Head in front of you. It's kind of like this."

I show him, my left hand the ocean, my right the rocky outcrop that's shaped for its name.

"You know it!" he says. "Are you staying there too?"

I'm full of excuses but before I can make them he's asking me to take a photo. "For my mum," he says. He can't be more than 18, 19. Just a boy, I tell myself. Be nice to him. By the time it's done I'm laughing and something about him has made me think I could do with the company after all. He's attractive in a clean kind of a way, like fresh air or your kid brother. And he's funny with it.

We walk on, comparing notes: how few people we've seen; how we navigated the mud on the path below Pendeen; how much we're looking forward to our baths.

At the rockpool below Gurnard's Head he says he'll swim. I'm tempted, but then he pulls down his shorts and I turn away, annoyed with myself for blushing.

"Maybe tomorrow," I say. "If it's warmer. I don't mind waiting, though. I'll show you up to the inn."

Looking at the back of him as he walks off, this interrupter of my solitude, I wonder how old he actually is. Whether maybe I've misjudged it and he's simply small for his age.

Because the tide is in, the rockpool's boundary has become the faintest of outlines that blurs with the ocean. He stands and swings his arms, twice, before diving a perfect arc and slipping under. He surfaces to shout about how cold it is, then he's swimming hard and fast and straight and this is when it happens.

He's exactly halfway across when I jump up and shout, "Oh Jesus! Oh Jesus!" as the body of a bull seal, all eight feet of its length and all three feet of its girth trembling, rears from the water and towers above this kid's head which is half-submerged in his front-crawl sprint. At precisely the moment the bull seal emerges, he executes a perfect underwater turn and swims back, moving twice as fast. He drags himself out and I run towards him but he only stands and says nothing, shaking the water from his ears. When I tell him, he laughs.

"Hey, chill out. There wasn't anything there."

"So why did you turn round when you did?"

"Because I'd had enough."

"But you were swimming so much faster. Why?"

"Because I'm hungry!"

"It was because of the seal. It must have been."

"Forget it," he says, pulling on his clothes. "You're imagining things."

I don't, though, and I carry on all the way to the inn, insisting he'd seen it. It's not until we meet later on that I realise how much I've annoyed him. I go down to dinner and find him standing at the bar, arms folded across his chest. I start to speak but he tells me to go away.

"Like I said, lighten up. And leave me alone, will you? It was bad enough having you following me all afternoon, but this whole seal thing's really out there."

Amazed, I see our meeting on the path from his perspective: a wholesale revision of my own. In the morning he's gone before breakfast, this kid who swam into a seal and denied it. As I set off for St Ives I pass the rockpool and wonder if he was right; if I'd imagined it all, rather than seen it.

But only for a moment and then he's there again: carving a furrow to the centre, flying not swimming, more bird than boy, oblivious.

'Every Contact Leaves a Trace' (Vintage) is published in paperback at £7.99