Nicole (Agnes Soral) is sent up the river for infanticide in this routine woman-in-prison feature. There she meets Marthe (Annie Girardot), a fellow murderess who receives special treatment from the warden Dessombes (Marie-Christine Barrault). The warden frames Nelly (Bernadette Lafont) for drug possession and has her thrown into solitary confinement. Sabien (Corinne Touzet) is a newcomer convicted of armed robbery who latches on to the lesbian Lucie (Milva), a longtime prisoner slated for release.

The French intelligence agency plants Xavier, a former militant leftist, into a fascist organisation called Janus, against whom Xavier bears an old grudge.

In a somewhat deflated story of robbery and deception set against the rooftops and byways of Paris, a group of enterprising petty thieves take advantage of the dog days of August to burglarize vacated apartments. At this time of year, all Parisiens are on vacation elsewhere, and the city is invaded by tourists on vacation from their own cities. In this mass rearrangement of the European population, the thieves get away with their looting until they run into an architect who catches them in the act. But his morals are nothing to brag about, as he gets more involved in what they are doing and wants some of their take. He is also smitten with one of the down-and-out women the thieves have been supporting (Dominque Laffin). As in so many French dramas, these conflicting relationships are doomed to be resolved only by tragedy.