'Sister' (Unrated)

Kacey Mottet Klein and Léa Seydoux in a scene from 'Sister'.

A ski-lift gondola, rumbling up the side of a Swiss mountain, is the means by which Simon (Kacey Mottet Klein), the 12-year-old boy at the center of Ursula Meier’s dark fairy tale of a film, gets to work.

His job: picking pockets, stealing boots and backpacks, taking money and even sandwiches from vacationers, and bringing his bounty back to the apartment in a public-housing high-rise that he shares with his adult sister (Léa Seydoux). That’s how they get by, he and Louise: He’ll hawk his wares, pocket the cash, share the food. As for Louise, who looks to be just a few years older, she’ll go off on dates with guys who pull up in cars, returning late in the night, or the next day.

Beautifully observed, and with a riveting and unstudied performance from Klein, Sister tracks its little thief as he prowls for loot — and crosses paths with strangers who hold out the possibility of friendship, of family. There’s a British cook (Martin Compston) working in one of the ski resort’s restaurants who reluctantly aids and abets Simon, and there is a well-to-do mother (a memorable turn from Gillian Anderson), there with her two children, enjoying the snow and sun. Simon, changing his name and his backstory, insinuates himself into her world.

Simon and Louise are like lost children from some old fable. They share a sense of isolation, an unspoken acknowledgment that life is moving apart from them. And they share something else unspoken, as well.

The official Swiss entry in the Oscar competition for foreign-language film, Sister is haunting and sad — and absolutely worth seeing.

Cast: Kacey Mottet Klein, Léa Seydoux, Gillian Anderson, Martin Compston.

Director: Ursula Meier.

Screenwriters: Antoine Jaccoud, Ursula Meier, Giles Taurand.

Ruth Waldberger.

An Adopt Films release. Running time: 104 minutes. Profanity, violence, adult themes. In French with English subtitles. Playing in Miami-Dade only: Cosford.