The Four of Us is a relationship drama involving two couples: the aspiring young journalist Janina (Nina) and her husband Ben, a struggling actor; and Janina's best friend Maria and Maria's boyfriend, the estate agent Nils. Four weeks previously, the four had agreed to a partner exchange, whereby Janina lived with Nils, and Maria with Ben, with an understanding that there should be no intimacy. The aim was that each should learn more about what they really want in a relationship. As the film opens, they gather at a holiday house by the beach on the North Sea to discuss their experiences. It soon becomes apparent that all four of them have broken the no-sex rule, and it appears that Ben and Maria are in love, and Janina is pregnant from Nils. Over the next two days they try to find a way of moving forward, other truths emerge, and it becomes clear that all of them have changed in their feelings and expectations of love.
Most of the film plays in the house and on the beach, and involves only the four main characters. Secondary characters appear only in the brief scenes in the city at the beginning and end of the film that show the protagonists in their everyday lives: Janina's colleague Anton and her boss Ann-Kathrin; Nils' clients, the family Bolschakow; an actress playing against Ben in a scene from a soap opera; and the staff at a clinic.