The film's protagonist, Janet, is a young student attending boarding school. After a number of nightmares concerning her mother, whom she saw kill her father when she was young, the girl is sent home to her guardian, Attorney Henry Baxter.
At home, she is assigned a nurse. Janet begins having more nightmares this time concerning an unknown woman with a scar and a birthday cake. The dreams get worse and worse. Finally, her guardian brings home his wife, whom Janet has never met. Janet is introduced to the woman at her birthday celebration.
The cake and woman from her dreams with the scar appearing at once is enough to make Janet snap. She kills the woman by stabbing her - the same way her mother killed her father. Janet is committed. Meanwhile, her guardian Henry and the nurse, who was disguised to look like the woman with a scar to drive Janet mad, celebrate the loss of Janet. However, the two do not go unpunished.
Who is taken in for questioning by the police?