Claire (Caroline Cellier) works as a supermarket cashier and lives with her 15-year-old son, Guillaume (Mathieu Crépeau), and her alcoholic husband, Claude (Niels Arestrup). Unhappy in her marriage, Claire conducts a secret extramarital affair with Laurent (Christopher Thompson), a wealthy and cynical younger man. Guillaume fiercely loves his mother and despises Claude's abuse, while also resenting Laurent's superficial treatment of Claire. During a violent domestic altercation, Claire kills her husband Claude. To protect his mother from imprisonment, Guillaume confesses to Inspector Guérin (Claude Brasseur) that he committed the murder himself.