Lars and Susanna have been married for twenty years. They love each other dearly and together they have forged a secure, happy existence with well-paid jobs, a large house, two cars and a daughter who is about to move away from home. Life has turned out just as happily and comfortably for Susanna's best friend Ann and her husband Ulf, who will also shortly be celebrating their twentieth wedding anniversary. One evening when the two couples are having dinner together, Susanna tells the others about an adulterous colleague. The story provokes strong reactions that cause a dramatic showdown among the couples. Susanna and Ulf think adultery is a natural, inevitable risk in any marriage. Lars and Ann completely repudiate the very idea of adultery and are shocked by the open-mindedness displayed by their other halves. After dinner Lars and Ann find themselves alone for a moment. Their rejection of infidelity has suddenly brought them closer. Perhaps they don't know their other halves as well as they thought? Or perhaps their marriages aren't nearly as happy as they had supposed? These questions send the two couples on an emotional journey that turns their lives and marriages upside down.