Sister, by the Franco-Swiss director Ursula Meier (Home), achieves its considerable effects at least partly by misdirection. Set during the Christmas season, it offers up a bitter irony in its French title, L’enfant d’en haut or The Child from On High, which helps steer the more simple-minded sort of movie-goer (and movie critic — see Manohla Dargis in the New York Times, for example) towards seeing the movie as a sort of political tract about that left-wingers’ favorite subject, “income inequality.” But it’s not really about income inequality at all, except insofar as such inequality betokens a much greater, much more serious kind of inequality: the moral and spiritual kind whose American counterpart has recently been adumbrated by Charles Murray in his book, Coming Apart.

Ms. Meier’s hero, 12-year-old Simon (Kacey Mottet Klein), lives in relative penury down in a Swiss valley with Louise (Léa Seydoux), his slutty ne’er-do-well older sister. There are vague and uncertain accounts of what happened to their parents. With the help of a season pass, Simon daily ascends on high to the posh ski-resorts above, in which god-like realm he steals and sells expensive ski-equipment to support his and Louise’s hand-to-mouth existence in the very different world below. To a certain kind of mind, the very presence — on film, at least, since the actual place would be read somewhat differently — of a playground for the idle rich, particularly when there is a clearly-drawn contrast with the less fortunate outside its boundaries, contains within its splendidly visual luxury an entire political narrative that scarcely needs spelling out. But beneath this obvious surface, Ms. Meier is actually doing something rather different and more interesting than illustrating why we ought to tax the rich.

For Simon, in spite of his larcenous career, is desperately trying to impose a strangely familiar moral template on his chaotic existence. Louise, who drifts from one menial job to another and often disappears for days at a time with some new man, is the more childish of the two and has come to depend on the money Simon brings in from his black market dealings to keep their little household intact. Simon willingly embraces the role of provider for them both and, in fact, actively subverts Louise’s attempts either to play a more responsible role herself or to bring an adult male protector into their relationship as a more appropriate head of the family, as she presumably sees it. Having assumed that role for himself, Simon doesn’t want to give it up to a stranger. Nor does he want Louise to break the bond of dependency he has established between them. So long as she needs the money he brings in to their cramped little apartment, so long will she have to trade for it the only love he has ever known.

There is one heart-breaking scene in which he offers her every penny of his ill-gotten gains in exchange for being allowed to lie down beside her in bed and cuddle. The otherwise bovine Louise understands well enough how the sexual economy works, even when there is no “sex,” as we and the movies habitually understand the term, involved. But there is a momentary consciousness, a distant memory perhaps, of the way in which custom once made use of its irreducible reality for socially more useful and emotionally more satisfying purposes. A similar moment comes to Simon when a rich Englishwoman (Gillian Anderson) mistakes him for another one of the rich kids at the resort and one who might like to play with her children. The awkward eagerness with which he tries on, as it were, the role of child rather than that of premature paterfamilias is equally touching.

Again and again he tries to imagine a way out of the grim necessity of the difficult and degrading but better-than-nothing life he has helped to make for himself and his sister out of desperately unpromising materials, and again and again he is unable to find the way. It’s almost as if the parody of the traditional family that the two of them have created has the family’s own gravitational pull on them — which to some extent it clearly does. Ms. Meier’s eye, and that of her director of photography, Agnes Godard, is therefore not so much on the gap between rich and poor as on what it stands for in terms of social cohesion versus social breakdown. I think she also sees how the moral force of traditional relations between the sexes, and between parent and child, somehow manages to reassert itself in even the most appallingly disordered circumstances and is not just a luxury that only the rich can afford.