Amid the blinding alpine light, 12-year-old Simon (Kacey Mottet Klein) scans the merchandise from behind ski goggles and a mask, his disguise in the Swiss film Sister. His name on the slopes is Julien. He nonchalantly takes skis, helmets, goggles, gloves, sunglasses and sandwiches from the racks and backpacks of a ritzy Swiss ski lodge. Their unseen owners chatter away in multilingual patter, oblivious to the thefts. Simon examines the merchandise in a restroom stall with all the diligence of a gypsy jeweller, throwing broken and worn items into the toilet before relaxing on the can with pilfered tea and sandwiches. Selling the goods to the neighborhood kids is Simon's job, while his unemployed older sister Louise (Léa Seydoux) zips off to drink with her various boy toys. They live together, without adult supervision. Mike (Martin Compston) is a British seasonal worker who gives Simon an expanded adult market for his wares. But when Simon meets Kristin (Gillian Anderson, Scully of X-Files fame), mother to two happy boys, he is moved to confront Louise about a series of lies that, when unraveled, will transform the way viewers examine the siblings' relationship.

Family and class dynamics are the key drivers in the aptly titled Sister. Louise can't hold down a job, so it's Simon's sales of "secondhand" ski equipment that buy the groceries—and fuel Louise's days-long binges with her boyfriends. She pays him back much later, by miserably plodding off to work as a cleaner. Social strata are physical. Above, either snow flurries or sun grace the rich who inhabit the Olympian paradise of Swiss ski resorts. Below, people like Simon and Louise live in a cramped apartment tower, the brown-and-flat expanse of the valley floor primarily devoted to churning factories and highways. 

Such a rigid duality, no matter how well-structured, is bound to put enormous stresses on whatever or whomever crosses the border, in this case Klein's Simon. If it weren't for the joyless expression on Klein's face as he sells his goods, it would be difficult to believe his character steals out of necessity rather than greed. And if it weren't for Klein's composed haggling with men twice his age, Simon would come off as immature. Klein, though, succeeds in his role as protagonist, thanks in no small part to the direction of Ursula Meier, who also worked with Klein in 2008's Home.

If there is an antagonist in Sister, it's Louise. We meet her as she steps out of a car, cursing at the driver and calling him a creep. "I'm tipsy, Simon," she says, walking home and urinating on the roadside. She lies to all her boyfriends, claiming Simon is temporarily staying with her. As an even bigger lie emerges, it's hard not to feel both revulsion and pity for her. Seydoux has got rage down pat, screaming, "You're a ball and chain!" at Simon repeatedly, but other emotions are a little flat.

The two are stuck with each other, and Sister's biggest success is avoiding mawkishness while still remaining, at its heart, an emotionally charged film that examines the faults and triumphs of broken families. After meeting Simon, Mike asks: "What about your parents? Haven't they got any money?" Julian replies, stone-faced: "I have no parents. Only a sister."

Critic's Grade: B

SEE IT: Sister opens Friday at Living Room Theaters.