In F. Scott Fitzgerald’s story “The Baby Party,” two supposedly civilized couples are quickly reduced to violence after their kids get into a fight. It only takes a crack for the veneer of polite society to shatter.

Something similar happens in Yasmina Reza’s Tony-award-winning play “God of Carnage,” which has been adapted into a movie with the blunter title “Carnage.” Two couples, refined and adult, are meeting in an apartment to discuss something that happened between their children. In the course of the movie’s 80 minutes, things do not go well.

In the perfectly composed opening credits shot, we see the children scuffling; one boy loses a couple of teeth in the altercation. Then the action moves to the Brooklyn condo owned by Penelope and Michael (Jodie Foster and John C. Reilly), who see their child as the victim of an attack.

They are hosting Nancy and Alan (Kate Winslet and Christoph Waltz), parents of the other kid. They’re a bit more upscale than Penelope and Michael, and, at least initially, more casual about the importance of this incident.

The shifting moods and alliances of this situation, which unfold in more-or-less real time, are entertaining and frequently funny, even if the movie never seems like the out-and-out “comedy” it’s billed as. In ordinary hands, with this set of top-line performers, “Carnage” would be a notable actor’s showcase.

In the hands of director Roman Polanski, who adapted the script with Reza, “Carnage” turns into something better than that. Polanski needs no introduction to the complexities of working in confined spaces, as “Rosemary’s Baby” and “Repulsion” proved, and he moves this quartet around this apartment as though they were animals in a cage.

Foster and Reilly are adept at drawing out the simmering hostilities that lie beneath their yuppified exteriors. Especially amusing is Christoph Waltz, the “Inglorious Basterds” Oscar winner, who devours with equal relish his cell phone, a serving of pastry and the snarkiest lines in the screenplay.

The way Polanski pushes these buttons, and orchestrates the dynamics of a single room, is seamless. If my eye isn’t fooling me, the director can also be glimpsed peeping out of a neighboring apartment, during one of Nancy and Alan’s periodic attempts to leave the place.

Mysteriously, Nancy and Alan can’t quite leave, although it would make sense to get out. If “Carnage” seems like a minor gem, a small-scaled mind-game, this aspect lingers: the way people stay in their cages, even when the exit is open. If Polanski is good at anything, it’s creating purgatories for people who stay too long, with dire consequences.

“Carnage” (3½ stars)

A skillfully oppressive adaptation of Yamina Reza’s Tony-winning play “God of Carnage,” with a sterling quartet — Jodie Foster, John C. Reilly, Kate Winslet and Christoph Waltz — acting out a disagreement in a Brooklyn apartment one afternoon. The material is small, but director Roman Polanski makes it seamless, and he knows how to make a purgatory out of a confined space.

Rated: R for language.

Showing: Alderwood mall, Metro, Pacific Place, Thornton Place.