Cracks
, the remarkably assured feature debut of Jordan Scott, daughter of Ridley, takes place entirely at an all-girls boarding school in 1934. The school is an imposing manor home isolated in the picturesque English countryside, with little black windows squinting out of a forbidding gray façade. The atmosphere inside is as oppressive and tense as you might expect. We see a morning service in the chapel, with scores of girls in identical uniforms singing a generic worship tune, while stealing nervous glances at the matrons glaring down sternly from their perch. We learn that the teachers read and vet the students' letters home – one girl is told to "try not to sound so down in the dumps."

The students' downtime is hardly more forgiving. Among the clique of girls we meet – members of the school's prodigious diving team – the cool, unflappable Di (Juno Temple) commands her peers with an iron fist. The self-appointed enforcer of the most trivial school rules (the girls are allowed to keep five things -- and only five -- on their nightstands), she struts across the grounds with a deceptively coquettish wiggle, favoring some with a smile and dismissing others with a roll of the eyes. She's a nightmare – like a character out of Mean Girls, except British, and there's nowhere to go to get away from her.

Enter Ms. G (Eva Green), beloved teacher and diving instructor. Beautiful, confident, liberated, unfailingly generous, she is worshiped by all, and none more than Di. She blithely breaks the rules, taking the girls out for nighttime skinny-dips, initiating whirlwind boogie-downs to "Puttin' On the Ritz," and assuring them that "the most important thing in life is desire" – which pronouncement is, of course, followed by some old crone lecturing the students on the dangers of "excessive ambition." Eva Green is breathtaking in these early scenes, combining free-spirited insouciance with an almost otherworldly elegance. It's easy to see why Ms. G is a favorite.

The established order is upended by the arrival of Fiamma (Maria Valverde), a Spanish aristocrat who has apparently been banished for a fling with a boy below her station. Fiamma – beautiful, confident, and a champion diver – immediately makes clear that she is not having any of Di's preening, imperious queen-bee nonsense. What's more, she quickly becomes the apple of Ms. G's eye, infuriating Di further. Halfway through Cracks, it's looking like war.

It's also, to be honest, looking a bit conventional – snobbish cliques, a vulnerable-but-steadfast hero, a sneering villain, goofy sidekicks (one of the girls is named Fuzzy, and her mopey clumsiness is played for comic relief), and an inspirational teacher who will show all of them what's truly important. Then, at roughly the film's halfway point, we begin to realize that Cracks is in fact doing something entirely different. There's no twist, but rather a gradual dawning that something here has gone seriously awry.

It is tempting to discuss the specifics, but part of why Cracks works so well is the way it sneaks up on you. What began as a fairly typical, flamboyantly British boarding school drama becomes a disturbing study of psychological distortion and arrested adolescence. At the center of the film's sinister turn, unexpectedly, stands the divine Ms. G, whose rousing stories of daring adventures in the Amazon may not be entirely truthful. (Eva Green handles the transformation beautifully – this is a towering performance.) Ultimately, Cracks is a rebuke to those who tout asceticism as a virtue. Isolation and self-denial can really screw with your head.

Jordan Scott redeems herself nicely from a technical standpoint – the movie is seamless and beautiful, with almost no hints of first-timer sloppiness (the only possible exception being an slight overemphasis on the slo-mo montage). But what really impressed me was its construction. Cracks transforms in front of your eyes from harmless and unassuming to menacing and genuinely disturbing. It's the year's most promising directorial debut.