The main combatants are two teenage sisters who find themselves on summer vacation at the French seashore with their gloomy parents. The older girl, 15-year-old Elena (Roxane Mesquida), is the shapely, pretty one, but some of her instincts are poisonous. Vain and impatient, Elena constantly snipes at the younger Anaïs (Anaïs Reboux), the dejected "fat girl" of the title, whose only defenses against soul-killing loneliness are her ill-formed sex fantasies and a plate piled high with potato salad. If anything, the girls' parents (Romain Goupil and Arsinée Khanjian) are even more insensitive to Anaïs' plight: Over breakfast, they casually devastate her with a few vicious words.
Breillat's climate of foreboding intensifies when the sisters meet an Italian law student named Fernando (Libero de Rienzo) in a café. Both girls are drawn to this older boy, putting a subtle new edge on their sibling rivalry, but he naturally chooses Elena as his next conquest. The extended scene in which the crude, young predator takes the reckless Elena's virginity, while her stricken sister pretends to be sleeping in the next bed, is one of the most disturbing things you'll ever see in a movie theater. "It's so easy with girls," the fumbling Fernando explains, as if to remind himself of the rules of engagement. For her part, Elena dares to think she's in love.
The intermittent love between Elena and Anaïs is a more complex thing; it's counterbalanced by real hate. Some Hollywood moviemakers build entire careers exploiting the insecurities of teenagers, but Breillat's grasp of the mutual need that binds the sisters (when it isn't tearing them apart) is so frighteningly accurate she puts to shame all those dime-a-dozen movies purporting to examine adolescent trauma. The frailty of the girls' self-esteem becomes everywhere evident -- in the self-hating ditties Anaïs sings to herself while absently wandering a windswept beach, and in Elena's desperate efforts to force the callow boy who's seduced her to actually love her. In their symbiotic moments, the sisters roll on a bed together, giggling at memories of their earliest antagonisms. Otherwise, they are consumed by resentment and envy. The sight of plump, desolate Anaïs rising out of a swimming pool in her sad green bathing suit may arouse pity in us; it arouses bitter contempt in her sister.
Breillat is not in the compassion business, as anyone who saw her controversial, ironically titled 1999 film Romance can tell you, and the final sequences of this bluntly powerful 86-minute film attest to that. Cutting short their vacation, the girls and their mother drive home to Paris in the family Mercedes, and from the start the apparently mundane trip feels as harrowing as a descent into hell. Huge trucks hem them in at every turn, and highway traffic itself takes on a threatening quality, underscoring the frazzled emotional states of the car's occupants. Even their stop for sandwiches at a rest area seems hazardous: Clearly, these are deeply unhappy people trapped in a web of dangers. Little do they know.
Breillat has coaxed beautifully detailed performances from her entire cast, but no one is likely to move you so much as young Anaïs Reboux, whose haunted fears are right there for all to see in the rolling contours of her doughy face, in her uncertain stride, in her fidgeting hands. When Anaïs sings tunelessly and abstractedly about a crow pecking at raw meat (as if she's predicting her bleak future) it's heartbreaking but thoroughly unsentimental. The greatest strength of this uncompromising film is its refusal to whine or mourn for trampled emotions; Breillat is more concerned with providing the cruel facts of life, unsugared.
That brings us to the matter of the film's title. In the original French, it's called A Ma Soeur, or To My Sister, which gives off markedly different vibrations than Fat Girl, and we are left to wonder who changed the title for the English-speaking markets, and why. (It's akin to renaming Cyrano de Bergerac as The Big-Nosed Halfwit.) But the complaint is relatively minor: Whatever the finished product is called, an unflinching, remarkably honest filmmaker has given us a terrifying glimpse into some misadventures of the mind and the flesh you won't soon forget.