Set at the fictional Montreaux School for Girls in Switzerland, the story centers on Dr. Stephen Dominick Herbert Marshall, the school’s popular director, who is secretly admired by Professor Anna Mathe Ruth Chatterton and by the 19-year-old French student Marie Claudel Simone Simon. At a state fair, the girls draw lots to see who gets to ask for a dance. Marie wins and nervously asks Dr. Dominick; because he believes it would be inappropriate to dance with a student, he refuses, leaving Marie in tears and running away, which makes her late for the bus back to the boarding school.
A week later, Professor Augusta Wimmer Constance Collier, a strict, unempathetic figure, combs through the belongings of her students and uncovers a discarded love letter. Dr. Dominick and Professor Mathe are tasked with identifying the letter’s author and quickly conclude that Marie Claudel wrote it, based on handwriting. Confronted with the accusation, Marie denies writing it, fearing the revelation of her crush on him. Some of the older teachers, including Wimmer, suspect that while she was away at the fair, she visited an actual boyfriend to whom the letter seemed addressed. With dating prohibited, Marie faces the real possibility of suspension just two days before graduation.
In tears, Marie confesses to Professor Mathe that she did write the letter. Anna does not reveal this to Dr. Dominick, but she does tell him that the girl is innocent. They both sympathize with her and try to shield her from punishment, yet the other teachers persist and even demand that her mother be summoned.
Desperate, Marie decides to run away into a storm. Dr. Dominick pursues her and catches up with her at a remote mountain hut. There, he brings blankets for her, and as they sit together, she confesses her feelings for him. He reveals that he feels the same way. The next day back at school, he proposes marriage, and she accepts.
Shortly afterward, Marie overhears a conversation in which Professor Mathe admits to being in love with Dr. Dominick and reveals she intends to leave the school because of heartbreak. To spare her, Marie lies to Dr. Dominick, claiming that she only told him she loved him to secure her graduation.
Not long after graduation, Marie is about to be driven home by her cousin Count Vallais [Tyrone Power] from a nightclub celebration, when Dr. Dominick arrives. He tells her that he could never fall in love with Anna Mathe, and the two share a kiss, marking the end of the tale with a bittersweet note of romance and unresolved tension.
