The film opens in a Swedish hospital where Karin Vergerus, a married woman in her late thirties, has come to view her dead mother. On her way out she breaks down and a man, obviously English, offers his help which she declines.

Karin is married to a surgeon Andreas and they live a comfortable life with their two children in a villa inherited from his parents.

David Kovac, the man who spoke with Karin, is an ex-patient of Andreas and is invited to their home for dinner. David is an archaeologist. He and Karin start an affair meeting in David's sparsely furnished apartment. David tells Karin about his past. His parents were Jewish and they lived in Berlin until he was 14, when they moved to Switzerland. All his relatives are dead except a younger sister. When Karin arrives late for one of their meetings he becomes violent, abusing her verbally and physically, telling her to return to her smug middle-class life. She leaves but he pursues her and the tense relationship continues. Several months later Andreas faces David with rumours about the affair he has heard about through anonymous letters he has received. David is aloof and tells him to rely on Karin's sense of loyalty to her marriage. Andreas is sympathetic to David, which he has felt since the first time they met after a failed suicide attempt by David. David denies his injuries were self-inflicted. The night after Andreas' visit, Karin stays at David's apartment but she cannot sleep and returns home. The next day when she is out shopping he intercepts her and Karin agrees to meet him at a church, an archaeological site he is excavating. In the church a statue of the Virgin Mary has been discovered that has been walled up for 500 years. The larvae of a dormant insect, brought to life by being brought out into the light, is destroying the statue from the inside. Karin tells David he is like a dangerous child to her. Although she could live as his mistress she cannot cope with his self-hatred. He leaves for London without saying goodbye. She pursues him there and finds he is living with his sister. The two are inseparable and Karin leaves.

Some months later he reappears in Sweden to inform Karin he has taken a post at a Danish University. He suggests they move there together. The ties of family life hold her back. He calls her a coward and they part for the last time.