While writing a screenplay about infidelity, elderly film director Bergman converses with an actress in an effort to help create the character of Marianne. Within his screenplay, successful actress Marianne is happily married to Markus, a conductor. They have a nine-year old daughter, Isabelle. Markus' best friend is David. Twice divorced, David is often at Marianne and Markus' apartment, and he is Isabelle's favorite storyteller. One night, while Markus is away, David visits the flat as usual. But something changes and what was once a safe, platonic friendship between Marianne and David is suddenly altered. Marianne now sees him in a different light, and finds him both sexually and emotionally attractive. Marianne enters into an affair with David, jeopardizing and ultimately losing her husband while painfully hurting her young daughter.