London at night, Captain Britain flies through he skies on patrol. A mad killer has been on the loose; a killer who strikes when the moon is full, like this night.
A lone woman walks the streets, when, suddenly, a monstrous figure leaps at her. Captain Britain joins the fray, seeing that the creature seems more animal than man. As it looks up and tears at Captain Britain, he realizes that it is a werewolf. The creature catches him off balance and leaps in for the kill… but misses. Cap grabs his star sceptre and gets to his feet, while the wolf man rips up a lamppost to wield as a cosh. As fast as thought, Captain Britain extends his sceptre to full length and uses it to ward off the wolf man’s blow.
The werebeast lunges at its original prey instead and hurls the girl into the Thames. Captain Britain instantly jumps after her. Free now from fear of attack, the monster turns, looks about and spies the weapon that defeated him. As he reaches for the sceptre, he recoils to hug his clawed finger in agony. For by the very power of its goodness, the sceptre has scorched the creature’s flesh. Seeing Captain Britain return with the girl, the monster leaps up the side of the nearest building. The creature has escaped and Cap leaves the girl to the police.
The next morning, at Thames University, Brian Braddock reads the report of last night’s horrors. The girl was the first victim to survive an attack. Now at last, the cops have a description. At least that way, Inspector Thomas can’t pin the attack on Captain Britain, Brian thinks wryly.
Courtney Ross, who is talking with a well-dressed, repressed-looking, bespectacled young man, calls Brian over and introduces him as Roddy, before correcting herself – Lord Kemp, who may enroll at Thames. And he has invited her to his ancestral home, Darkmoor Castle, for the weekend.
Brian and Kemp make friendly small talk. As they shake hands, Brian notices an unusual ring in the shape of a devil’s head on Kemp’s finger. It’s familiar and, suddenly, he remembers the werewolf wore a similar ring. Could a peer of England be a werewolf by night? But he can’t just blurt out an accusation, unless he reveals that he’s Captain Britain… Kemp doesn’t look like a homicidal maniac but, if Courtney intends to spend a weekend under the same roof, he will check Lord Kemp thoroughly.
The weekend rolls around and Lord Kemp’s sleek sports car drives Courtney to Darkmoor Castle, where they are welcomed by Hugo, the Kemp family retainer. Kemp gives Courtney a tour of the castle, showing her the antiques. As they pass a door, he warns her that, while she is free to roam the castle, she is to never to open that door. Is she in Bluebeard’s castle, Courtney jokes.
Later, in Thames University library, Brian has found out that the Kemp family has a long history of murderers, witches and feudal tyrants. For example, Rupert Kemp, 7th Baron Darkmoor, better known as the Black Baron, was accused of trafficking with the devil. Since his disappearance centuries ago, the castle has been closed to the public and little is known of his present descendants. If his hunch is correct, Brian thinks, his present descendant may be a werewolf. He changes into Captain Britain and flies off towards Darkmoor Castle.
Arriving there, Cap literally senses an aura of evil surrounding the stronghill. Suddenly, the castle’s stone gargoyles begin to move and fly toward Captain Britain to attack. The leading gargoyle spits out a searing gush of flame, which Captain Britain barely evades. He finds they are closing in from all directions. Any means of escape is cut off. He intends to go down fighting but is beaten senseless the next moment and plunges headlong towards the castle grounds.
Inside the grim walls, a figure long thought dead toasts a centuries old portrait of a beautiful blonde woman. The vampire announces that she was to be the bride of the Black Baron, had those fearful fools not burned her as a witch. But now he has found one who is her living likeness, one whom mankind will never take from him.
Moments later, the black-cloaked figure enters the bedroom where Courtney lies sleeping. Silently, he compares her with his dead love, Demelza, and comes closer intending to put upon her the kiss of the vampire.