After his wife Alice (Nicole Kidman) admits to having sexual fantasies about a man she saw briefly while the two were vactioning in Cape Cod, Dr. Bill Harford (Tom Cruise) is haunted by the idea of his wife being with another man. Pushed to an emotional brink, Bill finds himself in increasingly sexually charged situations as he succombs to an obsession with living out his fantasies. Eventually, Bill finds himself at a mysterious party at a huge mansion where masked participants engage in group sex. After being discovered as an outsider, Bill realizes that he is in over his head and that his life and marriage are in grave danger.