Lars and Susanna have been married for twenty years. They love each other and have created a secure, happy life with a daughter who is about to leave home. Life has turned out just as well for Susanna's best friend Ann and her husband Ulf, soon to celebrate their twentieth anniversary. One evening when the two couples are having dinner together, Susanna tells the others about an adulterous colleague. The story provokes strong reactions causing a dramatic showdown which turns their lives and marriages upside down.