The Gellhorn twins, Maria [Mary Collinson] and Frieda [Madelaine Collinson] have journeyed from Vienna to Karnstein in order to live with their aunt and uncle, Gustav [Peter Cushing] and Cathy [Kathleen Byron] Weil, following the death of their parents. Gustav Weil is a severely puritanical witch hunter who spends his nights searching out and burning the devil's servants--suspected witches and vampires. One of his greatest arch-enemies is Count Karnstein [Damien Thomas], said to practice the black arts and worship the devil.