Anna M, a shy, gentle young woman who is industrious at work and pleasant with her colleagues, convinces herself that a happily married doctor is in love with her. Every move this man makes, even his most virulent denials, are interpreted by Anna as evidence of his love. Carried away by her obsession, nothing can undermine her conviction: "He loves me!" Possessed by this imaginary love, Anna starts to glow...and respond to the doctor's "advances". She follows him, spies on him, steals his mail, writes to him, gives him gifts and calls him at all hours, night and day...But Anna's hope is followed by disappointment, resentment, then hate...