When Dr. Henry Jekyll (Ralph Bates) attempted to create an elixir of life using female hormones stolen from fresh corpses, he transformed into the gorgeous but evil alter-ego, Sister Hyde.
Sister Hyde's appearance is the source of jealousy by Susan Spencer (Susan Brodrick), a young woman who was in love with Jekyll. Jekyll referred to Hyde as his widowed sister.
The serum to maintain her female appearance required the use of female cadavers, which was obtained by murderers Burke and Hare. However, Jekyll soon found that he needed fresh bodies, and he began finding that in a number of London women.
Jekyll was being controled by Sister Hyde to commit the murders. Hyde seduced and killed Jekyll's good friend, Professor Robertson, after he began asking questions regarding the murders. Sister Hyde's agenda became clear that she planned to take full control and eliminate her male alter-ego.
To complete her plan, she set her sights on killing Susan, who was set to go on an opera date with Jekyll. Hyde followed Susan while she was out on her own. She was just about to kill her with a knife, when Jekyll regained control.
In the film's final moments, Jekyll committed another murder in an attempt to keep Hyde at bay. However, the police caught up to him. After Jekyll was led to a ledge on a building, he transformed into Sister Hyde, and ended up falling off to her death. She died in a deformed male and female hybrid.
- Martine Beswick appeared in the 1965 movie "Thunderball", as James Bond's contact in the Bahamas, Paula Caplan. In this movie, she was kidnapped by Fiona Volpe (Luciana Paluzzi), and later committed suicide by taking cyanide so she couldn't reveal anything to the SPECTRE agents.
- Martine Beswick appeared as Nupondi in the 1966 fantasy film, "One Million Years B.C.".
- Martine Beswick later portrayed the amazon Queen Kari in the 1967 film, "Prehistoric Women".
- Martine Beswick appeared as the Queen of Evil in the 1974 horror film, "Seizure!".
- Martine Beswick appeared as the mob boss Lana in the 1987 episode "The Color of Hammer" for the TV series "Sledge Hammer!".