Dr. Marcus John Carson calls Captain Kronos Horst Janson, an old friend from his war service, to his village where a string of deaths is marked by highly accelerated aging. Kronos and his hunchback companion, Professor Hieronymous Grost John Cater, are professional vampire hunters. Grost explains to the initially skeptical 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 and hints at a wider threat looming over the village.
Along the way, Kronos and Grost take in a local Romani girl, Carla Caroline Munro, who was sentenced to the stocks for dancing on the Sabbath. She repays the duo by helping them hunt the vampire and later becomes Kronos’s lover, bringing a human warmth to their grim quest.
Grost and Kronos conduct a mystical test that indicates the presence of vampires. Their findings are challenged by an eyewitness who claims to have seen “someone old, very old,” a contradiction that underscores the mystery and danger they face—if a youth-draining vampire should appear youthful, who or what is interfering with the hunter’s knowledge?
Marcus visits the family of his late friend, Lord Hagen Durward [William Hobbs], and speaks with Durward’s son, Paul [Shane Briant], and his sister Sara [Lois Daine]. He must leave before he can speak with the bed-ridden Lady Durward [Wanda Ventham], a woman whose frail appearance masks dangerous plans. While riding through the woods, Marcus encounters a cloaked figure that leaves him shaken, and he notices blood on his lips, a sign that the vampire’s influence may reach him as well.
In a tavern, Kronos defeats thugs led by Kerro [Ian Hendry], who were hired by Lady Durward’s coachman to murder him. Kronos, Grost, Marcus and Carla then set up a network of alarm bells in the woods to announce the passage of vampires, turning the countryside into a trap for the unseen predator. Meanwhile, a bat attacks and kills a young woman, a chilling omen that foreshadows the creeping danger.
Marcus realizes that he has become a vampire and begs Kronos to kill him. After attempts at 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 around his neck, revealing an ironic weakness that could be exploited.
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 Marcus. Grost forges the cross into a sword, while Kronos conducts a knightly vigil, a quiet ritual that prepares them for the confrontation ahead. After seeing the Durward carriage flee the scene of a vampire attack, Kronos suspects Sara as the vampire, a suspicion that will drive the climactic confrontations.
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 hypnotizes Carla and the Durward siblings. Lady Durward has raised her husband Hagen from the grave. She offers the mesmerized 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, breaking the enthralling hold she had over the Durwards.
The next day, Kronos bids Carla goodbye, before he and Grost ride on to new adventures, their quest ongoing as they confront the shadows that haunt the village and beyond.
