Scripter Brian Clemens had the highly imaginative idea of letting Robert Louis Stevenson’s 19th-century Dr Jekyll turn into a homicidal, glamorous Sister Hyde instead of the original hairy monster. He then pinned on him/her the responsibility for the Jack the Ripper murders.
Here, Jekyll, played by Ralph Bates, murders to remove organs needed for his experiments to prolong life and then gets his hormones wrong. Testing the drug he knocks himself out. Coming round he finds he likes himself as a glamor girl in the person of Martine Beswick and starts to get the best of both sexes when not killing. As male, he attracts the pure young miss living next door and as female fascinates her brother.
Director Roy Ward Baker has set a good pace, built tension nicely and played it straight so that all seems credible. He tops chills and gruesome murders with quite a lot of subtle fun. Bates and Beswick, strong, attractive personalities, bear a strange resemblance to each other making the transitions entirely believable.