An aimless young man is committed to a psychiatric hospital by his father in an attempt to cure him of his delinquent tendencies.

In the First World War, when Paris is expected to fall to the Germans, the attractive widow, Princesse de Bormes, organises a convoy of cars to evacuate the wounded from the front, and bring them back to her villa in Paris to recuperate. The authorities will not give them passes until an innocent 16-year-old boy, Guillaume Thomas de Fontenoy, joins them and is mistaken as the nephew of the popular General de Fontenoy. The Princess is enraptured by Thomas and her daughter, Henriette, falls in love with him. However Thomas feels impelled to see more of the action of the war.

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.

An old count hides just before he dies to annoy his heirs. The heirs search a manor for the count's body and are killed off one by one. Jean-Marie, his fiancée Micheline, and Edwige investigate the deaths and search for the count's body.