Plot

A man whose ancestors executed a witch is turned into a werewolf by modern-day descendants of the executed witch.

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.—Guy Bellinger

Prologue: It is medieval Transylvania. Irineus Daninsky has just slain Lord Bathory, head of a coven of witches and worshippers of Satan. His widow Elizabeth is holding a Black Mass in order to exact revenge when Daninsky and his troops crash the ceremony. Later, as the witches are all hung and Elizabeth is burned at the stake, she curses Daninsky. One of Daninsky's descendants will accidentally kill one of the Bathory descendants and set in motion a curse which will bring hell on earth to all succeeding generations of Daninskys.

Many generations later, Waldemar (the last remaining Daninsky) [Paul Naschy] is out in the forest hunting a wolf when he accidentally shoots a man (actually a werewolf). This sets in motion the curse, initiated by the man's family of gypsies, who select one of them, Ilona [Ines Morales], to infiltrate Daninsky's home and make him fall in love with her. One night, as Waldemar is traveling through the Borgo Pass on his way to Bistritz, his carriage comes upon a Ilona lying in the road. Waldemar cares for her at his castle until she is well. Waldemar's maid Malitza [Ana Farra] warns that Ilona is up to no good, but Waldemar has already taken her as a lover. On the eve of Walpurgis, Ilona takes a knife and a wolf's skull from her things, calls upon the dreaded Grey Shadow, slits her own wrist baptizing the wolf skull with her blood, and then presses the fangs of the wolf into Waldemar's chest, just above his left breast. Ilona then runs from the castle, where she is presently chopped up by the ax of insane murderer Janos Villeya, who has escaped from police custody and gone into hiding on Daninsky's land.

Some days later, as Waldemar is recuperating from his wound and suffering emotionally from the betrayal and loss of Ilona, he learns that an engineer named Laszlo Wilowa [Eduardo Calvo] from Budapest has just moved into the area, along with his blind wife Irina and their two daughters, Kinga and Maria. One day, as Waldemar is hunting for rabbit, he comes upon Kinga hanging from a cliff and crying for help. Waldemar helps her down, meets her family, including her precocious younger sister Maria. As the days pass, Waldemar finds that he is enjoying Kinga's company. Meanwhile, Kinga is falling in love with Waldemar.

One afternoon, Waldemar receives a note from Kinga [Fabiola Falcon] in which she asks him to meet her at an abandoned cottage near the mill. Just as Waldemar arrives, she is attacked by the insane murderer. Fortunately, Waldemar saves her, stabbing Janos in the stomach. As Janos runs off, Waldemar turns to Kinga, only to find that it is Maria [Maritza Olivares]. In an effort to upstage her older sister, Maria has decided to give her virginity to Waldemar. Waldemar tries to resist but, when Maria disrobes, he sweeps her into his arms. They make love, until the full moon rises and Waldemar suddenly changes into a werewolf and kills Maria. Malitza, who has been watching, drags Maria's body into the woods and leaves it to be found as yet another of Janos's victims.

Meanwhile, the mark of the werewolf (a red pentagram) has made its appearance on Waldemar's breast, and he has been changing into a werewolf on the nights of the full moon, during which he unknowingly kills some villagers. On the very night that Kinga tells Waldemar that she is pregnant, Waldemar kills her father. Blame for the killings has so far fallen on the escaped murderer, whom some say is a werewolf. Finally, Malitza explains to Waldemar what has been happening and tells him about the curse. Malitza promises to take care of it, so she reveals the truth to Kinga and gives her a silver dagger.

One night, some children playing ball discover Janos's body in an advanced state of decomposition. It becomes apparent to everyone that someone else has been doing the killing, and all eyes turn to Waldemar when they remember how he was marked by Ilona on the night of Walpurgis. The villagers decide to storm the castle and kill Waldemar. As the villagers, with their guns and torches and dogs, close in on Waldemar, Kinga gets to him first and stabs him through the heart with the silver dagger.

Epilogue: Five or six years have passed since Waldemar's death. Kinga and her son visit his grave, and we are reminded of Elizabeth Bathory's curse -- that it will extend to all of Waldemar Daninsky's descendents.

Original Synopsis by bj_kuehl.