Aunt Martha Proctor recalls to herself the evil that invaded her family's home, causing her to take desperate measures: One summer day, the Proctor family anxiously awaits the arrival of Dr. Dan Proctor and his invalid fiancée, Evelyn Heath. Dan's elder brother Douglas, a commercial illustrator, and his wife Ann are sympathetic toward Evelyn, whose troubled childhood spent under the dominance of an alcoholic father scarred her physically and emotionally. Upon arriving, the frail Evelyn is introduced to Douglas, Ann, their daughter Lee, houseguest Ernest Hackett, Aunt Martha and Douglas' model, Miriam Blake. Complaining of exhaustion, Evelyn then retires to her room and plays the melancholy strains of "Liebestraum" on the phonograph. That evening, Evelyn's shrieks pierce the house when Lee shows her a pet bird. Evelyn harbors a hysterical fear of birds, and to calm her, Douglas sketches her picture on the lampshade. After he leaves her room, Evelyn opens her diary and expresses her disdain for Dan and desire for Douglas. That Sunday, as the rest of the family attends church, Miriam and Douglas work in his studio. Desiring to be near Douglas, Evelyn is about to intrude on them when Dan returns unexpectedly from the hospital, and she accuses him of being insanely jealous of her. When Evelyn insists that Dan return to work, he meekly packs his suitcase and leaves. Envious of Miriam's relationship with Douglas, Evelyn next plots to exile her. She begins by poisoning Lee's mind against Miriam, leading the little girl to believe that Miriam is romantically linked with her father. When Lee passes her fears along to Hilda, the maid, Hilda tells John, the handyman, and Martha overhears the gossip. As a result, Martha suggests that Douglas take a vacation and send Miriam back to the city, but he ignores her. One afternoon, Douglas and Miriam drive to the train station to pick up a delivery of turpentine. When the two return home inebriated, long after dark, Hilda, scandalized, quits, and Ann questions her husband about his relationship with Miriam. Offended that his wife no longer trusts him, Douglas refuses to respond. When Miriam approaches Ann to explain, Ann slams the door in her face, causing Miriam to resign and leave the house. Evelyn then eagerly volunteers to take Miriam's place and Douglas naïvely hires her. One day, during a summer storm, Hackett returns to the house, having been alerted to the situation by Miriam. As Ann laments Douglas' heavy drinking, Lee descends the stairs, exhibiting Evelyn's neurotic symptoms. Realizing that Evelyn has sown the seeds of dissension in the Proctor household, Hackett urges Ann to force her to leave the house, but when Ann asks Evelyn to move in with Martha, Evelyn viciously accuses her of jealousy. When Douglas returns home, Evelyn hurls hysterical accusations at Ann and then breaks down in tears. Blaming Ann for Evelyn's condition, Douglas denounces her and storms out of the house. After gleefully watching Ann pack her bags and leave, Evelyn destroys the farewell note that Ann has left for Douglas. Soon after, Douglas returns, filled with recriminations, and becomes horrified when Evelyn begins to fantasize about their future together. Hurrying after Ann, Douglas apologizes, and they return to the house together. There, Douglas informs Evelyn that he is sending her to a sanitarium and instructs her to break off her engagement to Dan. Later, Evelyn phones Dan and the next morning, he appears, and Evelyn proposes that they immediately marry. Dumbstruck, Douglas finds the diary that Evelyn has placed on the desk and reads a passage describing her love for him. When Evelyn smugly suggests that Douglas read the last page, he turns to it and finds a passage denouncing her love for him. Convinced of Evelyn's sincerity, Dan decides to marry her and goes to pack some things. After he leaves, Evelyn stumbles upon Lee's empty birdcage, unaware that the bird recently died. When Evelyn becomes hysterical, Martha taunts her that the bird is flying free in the house. Panicked, Evelyn runs out screaming and plunges to her death from a cliff.