Turn-of-the-century London papers are filled with stories about a man being attacked by a female werewolf in a local park. Inspector Pierce of Scotland Yard is assigned to the case, although he tells Latham, his assistant, that he doubts the validity of such stories. Heiress Phyllis Allenby tells her fiancé, Harry Lanfield, that such rumors upset her, but the lawyer tells his intended not to worry, as she will move away from the park and into his home when they marry in one week. At the Allenbys' London estate, meanwhile, Martha Winthrop informs her daughter Carol that they are not related to Phyllis, as Carol believed, but were merely taken in by the Allenbys after the death of Martha's husband. Martha then warns Carol that they may be forced to leave the Allenby estate after Phyllis' marriage. The next morning, Phyllis awakens to find her hands covered in blood. Learning that a young boy had been killed in the park that night, Phyllis becomes convinced that she is afflicted with the Allenby werewolf curse. Phyllis locks herself behind the walls of the Allenby estate, refusing to see anyone, including Harry. Later, when Latham is murdered in the park by a mysterious female figure, Phyllis offers to turn herself in, but is stopped by Martha. Harry finally sees Phyllis alone, and she tells him all about the Allenby curse, but he discounts her fears as childhood illusions. The next night, Dwight Severn, an artist, is attacked by the she-wolf, but escapes with minor injuries. Harry then questions Carol about her relationship to Dwight, and she confesses that she has been secretly meeting him in the park most nights. Martha overhears their conversation and chastises her daughter once more for continuing her relationship with a penniless artist. Later, Phyllis confesses all to Carol. Carol tells her mother that she is going to the police, as she believes that Phyllis, rather than being insane, is the victim of a hoax. After Carol leaves the estate, Martha drugs Phyllis and tells her that she plans to kill her, as Martha committed the she-wolf murders in an attempt to drive Phyllis insane and maintain her position in the Allenby estate. Phyllis is saved when Martha catches Hannah eavesdropping, and the murderer is killed when she falls down a flight of stairs while chasing Hannah. Harry then rushes upstairs to inform Phyllis that she is finally safe from both Martha and the Allenby curse.