"The Lorna of the title is a young Albanian woman in Belgium who's just won her residency there. She has big plans—once her itinerant laborer boyfriend, who's jobbing it all over the E.U., gets in, they're going to open a snack bar together. All is hardly rosy, though, because Lorna got her residency via an arranged marriage to heroin addict Claudy (Dardennes stalwart Jeremie Regnier). The mobsters who got Lorna into the country and the marriage in the first place plan to kill Claudy with a fake overdose, after which Lorna will earn her freedom, and a big payday, by marrying a Russian in order to get him a residency. The efficient, organized, hard-working and seemingly pretty cold Lorna's plans start to go astray when Claudy makes a surprisingly good-faith attempt to straighten himself out. She's been looking at him as a rung on a ladder, but soon she's forced to recognize this genuinely meek and sweet fuckup as a human being.
The Dardennes' movies generally feature morally compromised protagonists who stumble onto the road to redemption without even knowing it. Their Lorna, played with exemplary quietude by Arta Dobroshi, succumbs to a kind of holy madness a little after the midpoint of the film, but in a very canny performing decision, she doesn't give any behavioral signs of that madness; she acts just as she has acted all through the film. It's just what she does that's different.
Critics often compare the Dardennes' films to those of Robert Bresson, but I'm not sure that's a terribly useful reference point any more. Their visual style is entirely more conventional (which is not to impugn its gracefulness); and while it wouldn't be true to say that Bresson wasn't as interested as story momentum as the Dardennes are, their approach to storytelling isn't as Bresson-inflectedly-idiosyncratic as some might tell you. Which is my hifalutin way of professing that Lorna is an entirely accessible film, one that moviegoers who like a nice juicy tale ought not be scared of."
I expanded upon some of my points writing about a British DVD of the film for The Auteurs: