Jack Russell discovers someone lurking outside his home. He confronts the stranger who introduces himself as Buck Cowan, a reporter researching the arcane book, Darkhold. He informs Jack that his father's castle was sold by his step-father, Philip, to one Miles Blackgar, who had it shipped to, and reconstructed on, his private island. Jack and Buck both suspect the Darkhold is now in Blackgar's possession, so they hatch a plan to take Philip's yacht to the island.
Buck poses as a hand working at the marina, and comes to ask permission to move the boat. When Philip insists on going along, Jack gets a head start and takes the craft out himself. That afternoon, he fights a squall and injures his head. Near the island, Jack's boat is boarded by a gunman who abducts Jack and scuttles the yacht.
He takes Jack by motorboat to the island where he meets Blackgar and his daughter, Marlene, as well as a terrified man who is knocked cold by the gunman, Garth. Blackgar explains he runs a mental institution and the man was an escaped patient. Inside, Marlene, never removing her dark glasses, tends to Jack's wound while evading questions about the castle, her father, his work, and especially, the Darkhold. They are interrupted when Blackgar calls his daughter assist with an emergency operation.
After being locked in a bedroom, Jack leaves through a window to explore the castle; he spies on the unorthodox surgery, then goes to the library where he finds the Darkhold. But with the rising full moon, he transforms into the Werewolf. He makes his way to the now empty lab and goes into a frenzy, destroying the equipment.
He then descends into the depths of the castle where Garth finds and fires at him. The Werewolf runs to find a door to a cell within which languish several misshapen humanoids, apparent failed experiments of Blackgar's. Freed by the man-beast, they attack and kill Garth.
Eventually, the Werewolf finds Blackgar, whom he throws out a window. Marlene enters the scene and appears grateful for her father's apparent death, and though she calms the Werewolf with her voice, when her fingers touch his, he recoils and lashes out at her, knocking her dark glasses from her face. Marlene now reveals herself to be a mutant with gorgon-like powers, as the Werewolf turns to stone. [TBC in WEREWOLF BY NIGHT Vol.1, #1]