Georges Deblache (Claude Brasseur), an aging, weary, and cynical 50-year-old police inspector in Paris, leads a lonely existence, filling his nights with alcohol and commercial sex work. His routine changes when he is paired with a much younger, attractive, and libertine partner, police detective Didier Théron (Nils Tavernier). Didier introduces Georges to his newly married, young wife, Barbara (Lio). Despite initial mutual hostility and tension, Georges becomes fixated on Barbara and takes advantage of Didier's prolonged absences to seduce her. The two plunge into a destructive, guilt-ridden extramarital affair marked by intense physical passion, emotional turmoil, and mutual psychological manipulation.