This gothic story of chilling suspense and psychological horror deals with two aging sisters, Jane and Blanche Hudson, who are living alone together in a Hollywood mansion. Jane, a former fair haired child star of early vaudeville known as "Baby Jane," was spoiled, pampered, and doted upon by her father, while her older sister, Blanche, was practically ignored as she lived in Jane's shadow. However, their roles were reversed after the death of their parents due to influenza, when both children moved to Los Angeles to live with an aunt. Blanche was favored for her dark hair and regal beauty, and was even encouraged to pursue a film career. Blanche became a star while Jane, who also worked in films, languished in her shadow. Blanche had a clause in her contract stipulating her studio make a picture with Jane for every picture that they made with Blanche.
At the height of her success, Blanche was paralyzed when her car crashed into the big iron gates in front of the mansion where she and her sister lived. They were returning from a party and Jane was drunk. When the police found her, Jane could not remember what happened. She was held responsible and accused of the attempted murder of her sister. Nothing came of the charge, but Jane's film career ended with Blanche's career.
Now, years later in 1959, Jane, a slatternly alcoholic who still dresses as if she is ten years old, and Blanche, disabled but still regal, continue to live together in the same mansion in a declining neighborhood. Jane resents having to live in the shadow of her sister, who became more famous than she ever was, and who is now being remembered because of a revival of her films on television. She hates having to cook, clean and care for Blanche, who is stuck upstairs in her bedroom, but has nevertheless managed to keep her good looks.
Blanche, whose only other contact with the outside world is Elvira Stitt, a weekly cleaning woman, and her telephone conversations with her doctor and attorney, realises she is growing old in the shadow of her mentally ill sister. She decides to sell her mansion and move them to something nicer and easier to take care of. She then calls her lawyer and tells him she is planning to sell. She hears the extension downstairs click.
Jane, who eavesdrops on her sister's calls, believes that Blanche wants to sell the house and put her away in a mental hospital. Blanche, who sees Jane's sinister, brooding mood swing beginning, tries to talk to her sister about her decision. Jane will not listen, however.
In a drunken daze, Jane decides to revive her childhood singing and dancing act of Baby Jane, reasoning that Fanny Brice had success with Baby Snooks. She then hires a musical accompanist, Edwin Flagg.
Themes include family secrets, resentment, hatred and deceit, and Jane's realization that she has gone from being the cute and beloved Baby Jane to old and unloved. The story culminates with an unusual twist.