Following the events in The Fury of the Wolf Man, the deceased lycanthrope Waldemar Daninsky is revived to life when two doctors surgically remove two silver bullets from his heart while performing an autopsy on him. Waldemar transforms into a werewolf, kills the doctors and escapes from the morgue. Some time later, two students, Elvira and her friend Genevieve, go searching for the tomb of medieval murderess (and possible vampiress) Countess Wandessa de Nadasdy. They find a possible gravesite in the vicinity of Waldemar Daninsky's castle, and he invites the girls to stay for a few days.
When Waldemar leads them to the grave of the countess Wandessa, Elvira accidentally revives her by bleeding on the corpse. The vampire woman turns the girls into creatures of the night like herself, and they roam the forest at night, killing people in eerie slow motion. Daninsky later turns into the Wolf Man, is forced to battle and destroy the vampire woman at the end of the film, and then is himself destroyed by Elvira, a woman who loves him enough to end his torment. (An interesting note - Naschy's real life wife of 40 years was named Elvira.)
Daninsky's lycanthropy is not given a specific origin in this film; the events of the film are assumed to have followed from the ending of Fury of the Wolf Man (1970), which involved a yeti's bite as the cause of Daninsky's curse. How Daninsky went from being a college professor in Fury to being a castle-owning count in Walpurgis is never addressed.
What does Daninsky turn into?
Wolf Man