While writing a screenplay in his secluded island home, director Bergman (Erland Josephson) interviews actress Marianne (Lena Endre) to help him as he writes the film, a tale of infidelity. Within his story, Marianne is an actress and happily married to orchestra conductor Markus (Thomas Hanzon). Often alone, the couple's friend David (Krister Henriksson) is a regular, welcomed visitor. One night, however, when Markus is away, Marianne and David start an affair, to disastrous results.