Jean-Paul (Alain Delon) is an out-of-work writer having an affair with Marianne (Romy Schneider), a successful journalist. As they frolic in a swimming pool in St. Tropez, she receives as call from the record executive Harry (Maurice Ronet). He arrives with his nubile young daughter (Jane Birkin). Harry and Marianne were once lovers and he makes a pass at her. Meanwhile, Jean-Paul makes a pass at Harry's daughter. After some drinking, Harry and Jean-Paul fight, resulting in Harry being pushed into the pool. Jean-Paul refuses to help the struggling man as he drowns, and the young couple tries to get their stories straight in order to avoid being charged with murder in this sometimes masochistic feature from France.