Although hardly more sanguine about working-class life than sibling writer-directors Jean-Pierre and Luc Dardennes’ earlier Rosetta and The Son, L’Enfant is a bit less claustrophobic. In those two predecessors, cinematographer Alain Marcoen’s handheld camera rarely left the orbit of the central character; here, the principal player isn’t even introduced immediately. The new movie also closes a circle with the Dardennes’ breakthrough, 1996’s The Promise, a bleak tale that nonetheless qualifies as their most hopeful. Both movies observe a young man’s relationship with an impoverished woman and her child, and in each, the man is played by Jérémie Renier. But whereas Renier’s teenage character quickly accepted the burden of doing the right thing, his grown-up alter ego automatically does the opposite.

L’Enfant opens with a woman returning to her apartment a few days after having given birth. This is Sonia (Déborah François), an 18-year-old who imagines her life will become more settled now that she’s the mother of baby Jimmy. Hardly. She discovers that her heedless boyfriend, Bruno (Renier), has sublet her apartment, leaving her homeless. Moving with so purposeful a gait that she briefly seems the film’s protagonist—who in a Dardennes film is always in resolute motion—she soon finds Bruno panhandling in traffic. Not inclined to keep a single coin in his pocket, Bruno has already spent the money he got for renting the apartment and returned to his usual sources of income. One of these is fencing stuff stolen by a small gang of elementary-school kids; when he goes to sell a video camera they’ve heisted, the buyer tells him she could also sell Jimmy. To Bruno, this sounds like a fine idea. As soon as he gets the baby to himself, he makes the deal.

Somewhat to Bruno’s surprise, Sonia doesn’t understand. He realizes that she won’t cooperate with his scheme to tell the police that Jimmy was kidnapped. Panicked, Bruno arranges to buy Jimmy back. But the dealers don’t simply want their money returned; they insist Bruno pay a significant penalty. “Only fuckers work,” Bruno tells Sonia, but now he has a full-time job: raising 5,000 euros before the baby peddlers kill him.

The money doesn’t really matter, at least not to the filmmakers. They’re less interested in the resolution of Bruno’s immediate dilemma than in the larger matter of his moral transformation, if that’s even possible. Yet L’Enfant is more of a thriller than any movie the brothers have made since The Promise, expanding the universe of the self-imprisoned Dardennes character to include cops and robbers. There’s a harrowing chase scene that leads to a climactic realization, as well as procedural details involving Bruno and his gang. The latter are among the narrative elements that explicitly recall Pickpocket, the closest thing to a slick crime flick in the portfolio of Robert Bresson, the Dardennes’ great inspiration.

Although the siblings would be lost making a conventional policier, their style is not entirely unsuited to the subject. Dardennes films are driven, fidgety, and wholly unsweetened, whether by music or sentimentality. Avoiding any hint of the picturesque—no one will ever consider arranging a tour of the brothers’ Belgium—the movies seem naturalistic and yet supercharged, despite the fact that the scenes usually play in real time. Whether inspired or simply intimidated, their casts are equally intent, giving performances of unparalleled urgency and tenacious focus. The result is far from conventional entertainment but still thrilling to experience.

The brothers prefer stark titles, but their last two have been less blunt than they seem: There were two sons in The Son, a dead one and a possible surrogate, and there are two children in L’Enfant, Jimmy and Bruno. But then, nearly everyone in the filmmakers’ universe is childlike in some way, whether because of pique, narcissism, or, in the case of Bruno, a sort of moral ignorance so pure that it’s almost indistinguishable from evil. Veterans of leftist documentary-making, the Dardennes are sometimes compared to social-problem directors like Ken Loach. The system the brothers decry, however, is operated by powers in the heart and the head, not at the IMF.