In France, the Mother Superior of a convent, and the convent's gardener, Pierre Cabeau, work with the French underground to help escaping prisoners of war. When an American pilot named John is shot down over France, he is directed by the underground to the convent's chapel. His appearance there startles Sister Clothilde, a novice who dislikes men, but she informs Mother Superior of his presence. Because he is carrying important information from the French underground intended for the English government, arrangements are made for John to pose as the shell-shocked husband of a local woman, Madame Bouchard, and escape to England using forged papers. Before he can flee, however, Nazi Major Krupp breaches the cloister and enters the convent grounds, frightening Clothilde when he threatens to take several girls for "service" unless John is found. Clothilde, who has not been outside the convent walls since she was eight years old, unintentionally reveals John's presence to Krupp.