Under the water he feels he is concealed, set free in the way that concealment allows. There, too, he finds that things formerly hidden are revealed to him; and as if to him alone. As a child he had the child’s fear of sea monsters, evil creatures of the deep. But now he is fourteen, and diving has helped him to put away childish things.

Down in the blue limbo, with the world’s unhappy surface left to itself and the seabed shadowy below – there, he worries for little more than the air in his lungs. And in this twilight world he feels a strange, new, delighting grace about his movement, gifted to him by a skill he hadn’t believed he could possess. He begins to feel special, capable. Not so apart as was feared, perhaps, from other fourteen-year-old lads who – he keeps hearing tales – are smoking and drinking and exploring sexual intercourse. Under the water, at least, another life starts to look possible: one in which he is a more considerable figure than his peers seem to believe.

They are done diving for the day; but Aaron Strang stands stock still on a rock, staring out at the spangles on the surface of the sea, waiting for Robbie to finish his one more go. Robbie’s like that – his stamina and appetite are simply of a higher order than Aaron’s. As smaller boys they learned to swim together, to hold their breaths together, to don mask, fins and snorkel together. But between the two of them Robbie is clearly the superior diver. To Aaron’s eye he just hits the water better – carving it apart then vanishing clean, the blue restoring coolly in his wake.

Aaron is in his wet trunks, a towel round his shoulders, rough against his skin. The high gorsy cliffs all around him form a basin of sandstone – an amphitheatre of a kind. The vast overhead has but a few stately clouds and a kittiwake whirling. All is quiet save for the shir of the sea and a low whistling wind.

Aaron shivers slightly; folds his arms. The haar, the old sea fret, is in the air. He can smell salt on himself, the pads of his fingers are puckered, his nipples small and purplish. He finds this sensuous, somehow.

But the longer he stares at the water, the more he is pervaded by unease he knows all too well. He can’t make it stop, not once this tide has come in: the special wistfulness of four o’clock. More than once in school his class have been told – and by Aaron’s own father – to write poems of the sea, paeans to the Dornoch Firth, the source of so much local piety. And never has Aaron come up with a single line fit for sharing.

The sea doesn’t care. It just doesn’t care what it does.

His strongest feeling, really, is that there’s something in the lapping of seawater – in its strong odour, and its steeping of his bare skin as he enters it – that stirs him in the region of his groin. But that’s not the stuff of sea-poems for reading out in class. He is a good pupil, but he doesn’t tell the truth at school, God forbid – he is the dominie’s son. Rather, he passes himself off, for it has long seemed essential to him that he give nothing away – not one bit of the fleeting strangeness in his head which, in fairness, doesn’t tend to outstay its welcome.

His feet teeter a little on the rocky crest. He imagines falling, into the sea, but this time swallowed whole, vanishing clean away – sinking and not resisting. Oblivion. The image in his head has a certain lonely appeal. But then Aaron imagines his throat glutted by saltwater, his lungs bursting … No: it pleases him to suffer only a little, a small measure under his mental command.

Now he hears a tread at his back but doesn’t react, plays it cool – a little mindful of his own moodiness, how it could look daft, him stood at the water’s edge staring out to sea like some loon in a storybook, some mystery lady with a windswept lover.

‘Aaron! Eh!’

He turns and Robbie Vallance is coming straight for him, bounding from rock to rock, covering the sort of terrain where Aaron would tiptoe. But Robbie never stumbles. For such a strapping lad he is awfully graceful.

‘Eh? What you thinkin’, ye gowk?’

Aaron only smiles, abashed. He and Robbie never have to say that much to get along: they are best friends, which is to say neither has met another body they like better, the local choices being what they are. Always they fall in with one another easily enough. ‘You up for such-and-such a thing?’ ‘Are ye up for it?’ ‘Aye.’ ‘Right enough then.’

Robbie has reached Aaron’s rocky crest, and gives him a friendly shove, such that Aaron struggles to keep his footing.

‘What are ye gawkin’ at?’

‘What’s it look like?’

‘Aye but why?’

‘Dunno. The sea. It’s like … it’s pure. Y’know? Pure just how it is.’

‘Pure bollocks,’ Robbie scoffs. ‘My da says a big load of shite gaes i’ the sea.’

Aaron laughs. No reproof; just the lightness pals have with one another. And that, he knows, is good for him. His pal Robbie is good for him.

Aaron’s da has called them ‘a fine pair’, which discomfits them both just a bit. But Aaron is quite sure he would sooner die than fall out with Robbie. While not minding his own company, Aaron has always known: You have to get along with someone. Solitude, if not intolerable, is somewhat disreputable. He has needed a friend with whom he can nearly be himself.

And Robbie, while made of more robust and outgoing materials, is also a fellow who will, at times, turn abashed at the talk of certain difficult things – will bite his lip a bit and say Aye, he’s bothered a bit by that an’ all. Aaron knows that with Robbie, as with himself, there is surely a lot going on under the surface.

They take up their bicycles and head home from the rocks, in the direction of the Vallance cottage, where they can expect a mug of tea and a piece. Aaron’s devout hope is only that Robbie’s visiting cousin Morag will have gone to her dancing lesson, and won’t be mooning about, trespassing on their leisure.

They follow the grassy coastal track north, above the sea, trundling a way by the ragwort and fireweed and harebells. Aaron’s eye is caught by a rock that intrigues him – a bit of jasper? – and he stoops to gather it for his collection, knowing, of course, that he won’t be asking Robbie’s view on it. Ever since the first occasion Aaron was moved to share his feeling for ‘interesting rocks’, Robbie has never quite let the oddness of the hobby pass without comment.

Still, it’s a fact: around the outcroppings of this coastal bluff Aaron has found what he can identify, courtesy of his father’s encyclopedias, as cretaceous rock fossils and gastropod shells. Each item in his collection is adhered carefully to a cardboard sheet, with a hand-inked marker. His father has been oddly unenthused by these studies; but then David Strang teaches geography – his son’s favourite class – nearly begrudgingly, as though it were an affront to the faith he professes less by churchgoing than by cryptic reference to theological tomes in his library, those bookshelves running all round the chalky walls of the Strang cottage. At any rate: Aaron knows how queer his private passion can appear to others, but it is a deep-lying part of a self that he plans one day to reveal.

Now the boys pass the schoolhouse, shut for a few days since it’s the tattie-planting time and the hands are needed. But a light is on within – Mr Strang, no doubt, sat there correcting exercises still, under his yellowed old map of the world, with the frowning brow on which veins are sometimes visible.

They pass the Ferry Hotel, and the painted gables of fishermen’s cottages. They pass the nature reserve, and the squat concrete outposts that are relics of the war. They pass, too, within sight of the implacable whitewashed church of the Reverend McVey, a kirk tall and pale like its incumbent, a plain cross set high atop the birdcage bellcote.

And then the big Gallagher property – the old stone fortress remodelled as a handsome home for a moneyed man’s family, the perimeter of its long garden rolling powerfully down the incline toward rocks and sea. Aaron knows that Robbie’s gaze will scour that lawn and that facade as they pass – he will be after a glimpse of Marilyn Gallagher. But Aaron also knows better than to tease. Girls tend to look at Robbie a certain way, as if he were something to consider, and Robbie is surely right to be pained that the girl he likes best won’t pay him the same homage.

Aaron’s sense of his own looks? A troublesome business. He sometimes feels he sees himself, painedly, in the plate section of his biology textbook: a little neanderthal caveman, albeit too lithe and bony to have survived long as a hunter-gatherer. When he tries out his smile in the...