Set in what seems to be 19th century Eastern Europe, old and frail Professor Abronsius (Jack MacGowran) and his inept and withdrawn apprentice Alfred (Roman Polanski) are on a mission to prove the existence of vampires. They eventually reach a town and stay at the local inn only to find that the inhabitants have certain rituals to ward off evil.
While there, Alfred meets the inn-keeper’s daughter, Sarah (Sharon Tate) and becomes very fond of her before seeing her being kidnapped. The kidnapper is Count von Krolock (Ferdy Mayne) and when Sarah’s father, the inn-keeper Yoine Shagal (Alfie Bass), learns what has happened he sets off to rescue her but is himself captured and turned into a vampire.
Abronsius and Alfred set off in pursuit of Krolock through the snow following the trail that takes them to his castle in nearby hills. As they steal into the castle they are captured by Krolock’s hunchback servant, Koukol (Terry Downes) who takes them to the Count. He, however, seems hospitable and after questioning them about the reasons for coming to his castle invites them to stay, but neglects to tell them about a ball he is holding the next night where new vampires will be made.
Shagal, now a vampire is no longer bothered about freeing his daughter and is more intent on turning Magda, a maidservant at the inn, into his vampire bride.
Although unsure about it, the Professor and Alfred accept the invitation but Alfred has a restless night. He discovers Sarah, not yet ‘vampirised’, but she doesn’t want to be saved yet as she wants the opportunity to wear a ball gown.
The Professor, however, is set on destroying the Count by driving a stake through his heart so he and Alfred set off to find the castle crypt. This is guarded by Koukol so they have to find another way in. They find a window but unfortunately Abronsium gets stuck so Alfred has to be the one to kill the Count while he’s still asleep. In the end, though, he couldn’t do it as his nerves got the better of him so he goes back to try to free the Professor.
After freeing the Professor they go back into the castle. While searching for Sarah, Alfred meets Herbert, the Count’s homosexual son, who tries to seduce him. Herbert is a vampire and tries to bite Alfred who with the Professor beats a hasty retreat down a dark stairway to what they think is safety. However, they are now trapped in a turret where they witness gravestones opening and vampires galore coming out. It appears that the Count provides the victims for them once a year and he tells the Professor and Alfred that this is their fate.
The Professor and Alfred manage to escape and go to the dance in disguise. They rescue Sarah and escape by horse and carriage thinking that they have succeeded in their mission. Unfortunately they haven’t and Sarah wakes up and bites Alfred.