Few contemporary filmmakers can tell a story as well as Jean-Pierre and Luc Dardenne, whose gripping features all take place among marginal people in a nondescript French-Belgian industrial city. In La Promesse (1996), Rosetta (1999), The Son (2002), and now this volatile 2005 drama, the camera sticks close to the protagonists but neither the plot nor the characterization is ever simpleminded. Jeremie Renier (La Promesse) plays a petty thief who sells his newborn son, then struggles to buy him back after the mother recoils from the deed. Whether the title refers to the baby or the thief remains an open question, and the viewer is left to decide whether the theme of redemption should be perceived in Christian terms. This builds to a suspenseful climax, and as in Hitchcock’s best work, that suspense is morally inflected. In French with subtitles. R, 100 min. Century 12 and CineArts 6, Music Box.