The film is a road movie that follows a middle aged man who gives a young woman a lift. On the car radio, news bulletins warn the population against a recently escaped sadist who is known to prey on young women and children. Lelouch often cuts away from the main story, if only briefly, to parallel events that are not necessarily crucial to the story but illustrate what is suggested by the radio.

Thérèse is living in a provincial town, unhappily married to Bernard, a dull, pompous man whose only interest is preserving his family name and property. They live in an isolated country mansion surrounded by servants. Early in her marriage her only comforts are her fondness for Bernard's pine-tree forest, which was her primary reason for marrying him, and her love for her sister-in-law and Bernard's half-sister, Anne. The movie recounts in flashback the circumstances that led to her being charged with poisoning her husband.