Karin, a recently released mentally sick young woman, is spending her vacation with her husband Martin, a doctor, her father David, a writer just back from Switzerland, and her younger brother Fredrick. Karin seduces her 17 year old brother when he confesses he has never had sex. Karin is suffering from hallucinations and hysteria. She thinks she is visited by God.
Bergman's mastery with actors (there is absolutely never a bad performance in a single one of his films) and with the cinematic form (using space and mood to communicate his theme) is abundantly clear here.
Deservedly winning the 1961 Foreign Language Oscar, this gloomy and intense family drama, set on a romate island, is the first in a trilogy that explores issues of religion, faith, and human fraiglity.