Jane Hudson, a former child star known as "Baby Jane," lives with her sister, Blanche, a once-famous actress who is now wheelchair-bound due to a mysterious accident years earlier. Jane, filled with resentment and deeply affected by her lost childhood fame, becomes increasingly unstable and hostile towards Blanche. She begins to isolate her sister, depriving her of basic needs and tormenting her both mentally and physically. The household is filled with tension, and Jane’s erratic behavior emphasizes her gradually deteriorating mental state. Adding to the strain is the fact that Blanche’s career had eclipsed Jane’s, a point of deep bitterness for Jane.

As Jane's psychological torment intensifies, Blanche seeks ways to escape and alert the outside world to her dire situation. However, Jane’s paranoia and violent tendencies make this nearly impossible. The film explores themes of envy, regret, and the effects of long-standing grudges within a toxic sibling relationship. Throughout the movie, suspense builds as the true nature of the sisters’ past and the accident that crippled Blanche slowly come to light. Jane's descent into madness and Blanche's desperate plight create a gripping narrative, leading to a climactic confrontation that reveals shocking truths about their lives.