In 19th Century Europe, identical 19-year-old orphaned twins Maria (Mary Collinson) and Frieda (Madeleine Collinson) Gellhorn arrive in the small village of Karnstein. One of them is good, the other is bad.
Frieda is initiated into a vampire cult, and a number of deaths sweep the area.
The twins’ guardian – the puritanical Gustav Weil (Peter Cushing) – heads up a vigilante group called ‘the Brotherhood’ who conduct witch hunts and have vowed to end the threat of vampirism.
Frieda is captured by Weil and ordered to be burned, but the slightly camp vampire Count Karnstein (Damien Thomas) swaps the girls over and it is the innocent Maria who is set to face the flames.
Mary and Madeleine Collinson were Playboy models from Malta and had thick Maltese accents. As they had done with other foreign actors, Hammer simply had their dialogue replaced by British performers.