When his village is plagued by mysterious deaths marked by highly accelerated aging, Dr. Marcus calls in his army friend, Captain Kronos. Kronos and his companion, the hunchback Hieronymus Grost, are professional vampire hunters. Grost explains to the initially sceptical Marcus that the dead women are victims of a vampire who drains not blood but youth, and that there are "as many species of vampire as there are beasts of prey." The discovery of another victim confirms Grost's explanation. Along the way, Kronos and Grost take in a local barefoot girl, Carla, who had been sentenced to the stocks for dancing on the Sabbath. She repays them by helping them hunt the vampire; she later becomes Kronos' lover.
Grost and Kronos conduct a mystical test that indicates the presence of vampires. Their findings are contradicted by an eyewitness who claims to have seen "someone old, very old", whereas a youth-draining vampire should appear youthful.
Marcus visits the family of his late friend, Lord Hagen Durward, and speaks with Durward's son, Paul (Shane Briant), and his beautiful sister Sara (Lois Daine). He must leave before speaking with the bed-ridden Lady Durward. While riding through the woods, Marcus encounters a cloaked figure that leaves him shaken, and he finds blood on his lips.
At a tavern, Kronos defeats thugs led by Kerro, who were hired by Lady Durward's coachman to murder him. Kronos, Grost, Marcus and Carla set up a network of alarm bells in the woods to announce the passage of vampires. Meanwhile, a large bat attacks and kills a young woman. Marcus realises that he has become a vampire and begs Kronos to kill him. After various methods (including impalement with a stake and hanging) fail, Kronos accidentally pierces Marcus's chest with a cross of steel that Marcus had been wearing round his neck.
Having thus determined the vampire’s weakness, Kronos and Grost obtain an iron cross from a cemetery. They are accosted by angry villagers who believe that they murdered Dr. Marcus. Grost forges the cross into a sword while Kronos conducts a knightly vigil. After seeing the Durward carriage flee the scene of a vampire attack, Kronos suspects Sara as the vampire.
Carla seeks refuge at Durward Manor to distract the household while Kronos sneaks inside. The "bedridden" Lady Durward reveals herself as the newly-youthful vampire, and she hypnotises Carla and the Durward siblings. Lady Durward has raised her husband Hagen from the grave. She offers the mesmerised Carla to her husband, but Kronos erupts from hiding. Kronos uses the new sword's mirrored blade to turn Lady Durward’s hypnotic gaze against her. He kills Lord Durward in a duel, and then destroys Lady Durward.The next day, Kronos bids Carla goodbye, before he and Grost ride on to new adventures.