Guðmundur Arnar Guðmundsson makes a promising debut in this tender, slightly lopsided study of teenage friendship and inchoate sexuality.

There’s a vast, storm-hued majesty to the jagged coastal edges of Iceland that inspires hushed awe in tourists, armchair travellers and filmmakers alike, but to a teenager growing up — and, more trickily still, coming out — in this brooding idyll, it can seem like a smallest place in the world. That’s the cruelly frustrated perspective shared by two best friends in Heartstone, at least until they realise that they’re no longer experiencing the same coming-of-age crisis. Richly atmospheric the film toggles its main characters’ arcs for a stretch, before giving preferential treatment to the less dramatically challenging of the two. Still, first-time feature director Guðmundur Arnar Guðmundsson steers proceedings with enough serenity and sensitivity to soften stonier hearts in the arthouse market.

In its positioning of the rural Icelandic landscape as a kind of silent, ever-present antagonist to its principals’ progress, Guðmundsson’s formally imposing debut visually and tonally recalls the work of his compatriot Runar Runarsson — whose own somber 2015 coming-of-ager, Sparrows, deployed similar physical terrain to much the same emotional effect.

The boys’ conflicted, even hostile, relationship to their environment is viscerally symbolised in a startling opening scene, which in which 14-year-old Thor and Kristján, together with a group of pals, savagely cull a school of fish in the local dock, plucking them from the water and bashing their heads on dry land. This kind of hormonally fevered destruction is what passes for fun in their sleepy maritime village, where Thor lives with his single mother — who has recently, to her children’s aggrievement, re-entered the dating scene — and two older, somewhat bullying sisters. Kristján, meanwhile, weathers a consistent stream of abuse from his hard-drinking dad.

While the two boys have a supportive social circle (including some girls with whom they make halting attempts at romance), it’s clear that they’re the most important people in each other’s lives. Tall, sturdy Kristján, already accelerating into manhood, acts as something of a protector to the less mature, none-too-aptly named Thor — who, in one of several wry observations on the occasional tedium of adolescence, fashions a merkin from hairbrush debris as he waits for his pubic hair to grow in.

But as the kids horse around and venture into tentative sexual explorations, it’ll become clear to audiences — if not quite yet to Thor himself — that Kristján’s devotion to him isn’t purely platonic. For many LGBT audiences, such inchoate, unrequited desires will register as a familiar rite of passage. Guðmundsson maps the subtle, even subconscious, strain this development places on the relationship with tact and intelligence, aided by the open, naturally expressive performances of his two young leads. But as the film drifts further into Thor’s not-quite-comprehending headspace, Kristján recedes into the background, even as his character negotiates a compelling maelstrom of warring feelings and external obstacles — including the homophobia of his own parents, as adulthood comes with its own limitations in this stymied community. To quote an Emiliana Torrini song that Thor’s sisters blissfully listen to: “If it’s so good being free/Would you mind telling me/Why I don’t know what to do with myself?”

Sympathetic as Thor’s journey to awareness is, Heartstone’s languid, rollingly repetitive storytelling never quite justifies its weighted focus on his character at the expense of his friend’s more active anguish; a more judicious edit could place both in sharper relief. (The question of how assured Thor is of his own nascent sexuality, meanwhile, is only skirtingly addressed.) Later, Guðmundsson returns to the fish motif in slightly more contrived fashion, as a bullrout is briefly taken from the water and thrown back in, plummeting briefly before finding its gills. Not everyone in this thoughtful, lyrical, slightly over-deliberate tour of a beautiful teenage wasteland gets his own sink-or-swim moment of catharsis.