There’s always an undertow of melancholy even to the most idyllic of summer vacations. Every blissed-out day that passes is another closer to it ending, and the shadow of normal life resuming — with its work and school and domestic obligations, shelving the freer, looser personae we adopt away from home — hovers beside our pleasure like a glum weather forecast. That’s what makes them such a good subject for movies: They offer characters escape and adventure on a restlessly ticking clock. In “Aftersun,” for a depressive young dad at a Turkish resort with his pre-teen daughter, the pressure to maximize that time out of reality only draws the reality nearer; Charlotte Wells’ sensuous, sharply moving debut shows that no amount of pool time and fruity drinks and Macarena dance-alongs can keep either the past or future at bay.

Among the more crisp, confident first films to emerge from the British independent scene in of late, “Aftersun” confirms the sly, angular promise of Wells’ shorts, which put the Scotswoman on the map at such festivals as Sundance and South By Southwest — and secured her some enviable collaborators for her shift into features, with Barry Jenkins and Adele Romanski, no less, among the film’s producers. Their involvement will significantly boost the international profile of this modestly scaled Cannes Critics’ Week premiere, as will the presence of Irish star Paul Mescal — fresh from a BAFTA win for his breakout turn in TV’s “Normal People,” and here proving himself a compelling big-screen presence, probing an anxious, uneasy flipside to his casual, laddish charm.

Not that it’s a solo spotlight: “Aftersun” hinges on a remarkable duet between Mescal and 11-year-old newcomer Frankie Corio as a single father and daughter revealing new, vulnerable facets of themselves to each other over the course of a tacky package vacation at the tail-end of the 21st century. 30-year-old Irishman Calum (Mescal) is frequently taken for the older brother of his inquisitive, tomboyish daughter Sophie (Corio), and sure enough, there’s an edge of sibling-like complicity to their relationship, with their shared oddball jokes, loose conversational comfort with each other, and mutual resistance to patriarchal tradition. Based in London, Calum is also an irregular parent to Sophie, who lives in Glasgow with her mother — her parents’ past relationship evidently ancient history.

That lends an additional urgency to the trip Calum has booked for them at a family-oriented Mediterranean resort populated almost entirely with braying, sunburned Brits: As a rare period of sustained father-daughter time, it’s a chance for both Calum and Sophie to prove themselves to each other, showing off their responsibilities and capabilities, respectively. And for the most part, they have a good time, whether sunbathing together, shooting pool, sharing a laugh at the cheesy in-house entertainment or playing around with a camcorder that occasionally, accidentally captures Calum in more morose repose. Wells’ taut script tells us little of his life outside the immediate present, but stray asides and moments of solitary rumination — a fretful cigarette on the balcony when he thinks his daughter is asleep, a longing fixation on a Persian rug at a local market — hint at nagging unhappiness beneath the surface, as do furrows of worry and unrest at the corners of Mescal’s otherwise bluff performance.

Perceptive if not overly precocious, Sophie notices some of her dad’s mood shifts, but is distracted with growing pains of her own. Boys are showing an interest in her for the first time, while she’s developing the halting self-consciousness of any kid crashing into adolescence, putting away some childish things but not others, to dissonant effect. With both father and daughter privately facing their own fears of getting older, there’s a sense that they may never share this innocent, breezy ease with each other again. “Aftersun” thus works elegantly as a kind of dual coming-of-age study, perfectly served by Mescal’s signature brand of softboi gentleness — here shown maturing and creasing into more hardened, troubled masculinity — and the vitality of Corio, whose deft, lovely performance braids both authentic exuberance and a girlishness that feels more performed, as if for the benefit of her dad. In one extraordinary scene, her insecurities seep out during a brave-faced karaoke rendition of, of all songs, R.E.M.’s “Losing My Religion” — three minutes that appear to age her by three years.

It’s one of several ’90s British radio standards that fill the soundtrack of “Aftersun,” from the rasping indie rock of Blur and Catatonia to the caramel pop groove of All Saints. Yet there’s more to the film’s balmy summer-of-’99 setting (immaculately evoked by Gregory Oke’s primary-colored, faintly sun-bleached lensing, as well as canny production and costume design) than empty remember-this nostalgia. Temporal glitches and brief, non-specific flashbacks keep breaking into the vacation time, as Wells and editor Blair McClendon obliquely loop proceedings both back to Calum’s more carefree salad days, and forward to Sophie’s own edge-of-30 adulthood, drawing a wavy, hazy line between the anguish of father and daughter.

We’re left to color in the intervening decades ourselves, though it’s hard not to assume time has brought greater distance and belated understanding to this relationship. Ambitiously and poignantly, “Aftersun” explores the oddly intimate chasm between parent and child, the latter forever playing catch-up to the former’s inner life, except on the brief occasions — like, say, a summer vacation — when they can both be children for a moment.