In London at the beginning of the twentieth century, Phyllis Allenby is a young and beautiful woman who is soon to be married to barrister and boyfriend Barry Lanfield. Phyllis is living at the Allenby Mansion without the protection of a male, along with her aunt Martha and her cousin Carol and the servant Hannah. As the wedding date approaches, London is shocked by a series of murders at the local park, where the victims are discovered with throats ripped out. Many of the detectives at Scotland Yard begin murmuring about werewolves, while Inspector Pierce believes the opposite and suspects strange activity at the Allenby Mansion (which is near the park), where the "Wolf-Woman" is seen prowling at night and heading for the park.

Phyllis becomes extremely terrified and anxious, since she is convinced that she is the "Wolf-Woman", deeply believing in the legend of the so-called "Curse of the Allenbys". Aunt Martha tries to convince Phyllis how ridiculous the legend sounds, while she (Aunt Martha) and Carol are suspicious in their own ways. Phyllis each day denies Barry visiting her, and when a suspicious detective is murdered soon after he visits the mansion in the same way the other victims perished, Barry begins believing that something else is going on beside the so-called "Werewolf murders", and makes his own investigations both of the park and the mansion. It turns out that Aunt Martha did the attacks to convince Phyllis she was insane, and belonged in an asylum rather than married to Barry, so Martha and her daughter could remain living in the mansion.