Curse of the Devil (1973)

Great Inquisitor Ireneus Daninsky has Countess Bathory burned alive and her female followers hanged. Before perishing in the flames, the countess puts a curse on Daninsky and his descendants. Four centuries later, Waldemar Daninsky accidentally shoots a gypsy while hunting a wolf. The angry gypsies, who knew of the curse, summon Satan, and the beautiful Ilona is chosen to seduce the young lord. During a night of love, Ilona bites Waldemar, who turns into a werewolf and kills prey on full-moon nights. His murders are at first attributed to a mad killer who has escaped from the asylum. Waldemar, who suspects the killer is none other than himself, falls in love with Kinga, the daughter of a professor from Budapest. When Maria, Kinga's jealous younger sister, manages to seduce Waldemar and sleep with him, she is killed by the young man when he turns into a werewolf again.