In Germany in 1910, Vandorf bears the shadow of seven murders committed over five years, with every victim mysteriously turned to stone.
In an old millhouse tucked away in a forest, Sascha Cass Toni Gilpin reveals to her artist boyfriend Bruno Heitz Jeremy Longhurst that she is carrying his child. Bruno, trying to shoulder his obligations, races off into the night to see Sascha’s father, despite her pleas for him to stay. Sascha hurries after him, but loses him in the dark woods. There, she confronts a creature, gazes into its face, and dies. Dr. Namaroff Peter Cushing, a brain specialist at Vandorf Medical Institution, examines the body and confirms that Cass has turned to stone, while Bruno is later found hanged in the forest. An inquest concludes murder and suicide by Bruno, and Namaroff withholds Cass’s fate from the court.
The villagers, robbed of a clear answer, turn their ire toward Bruno’s father, Jules Heitz Michael Goodliffe. Police warn Jules to leave Vandorf, but he refuses to depart until Bruno’s name is cleared. Heitz suspects a conspiracy of silence and believes the murders spring from something inhuman, a force tied to ancient mythology. He contends that a vengeful spirit haunts Castle Borski—the Gorgon Megeara Prudence Hyman—a monster whose gaze can turn living flesh to stone.
To uncover the truth, Jules reaches out to his friend, Professor Meister Christopher Lee of Leipzig University, who also serves as Paul Heitz’s tutor. Paul leaves his studies to travel to Jules. That night, Jules is drawn to Borski Castle by a psychic summons and, upon glimpsing Megeara’s face, staggers back to the millhouse, where, while turning to stone, he manages to write a letter to Paul mentioning Megeara. Paul arrives to learn of Jules’s death, and Carla Hoffman Barbara Shelley, Namaroff’s assistant, visits the millhouse and discreetly reads Jules’s letter, later recounting what she can remember to Namaroff. Warden Ratoff Jack Watson reports that Martha, a violent inmate, has escaped the Institution, and Namaroff reveals to Carla that Megeara’s spirit exists and can possess a human.
That night, Paul is drawn outside by an eerie sound and glimpses Megeara’s reflection in the garden pool. He awakens five days later in the Institution, aged by ten years. Determined to stop the menace, Paul returns to the millhouse to confront the danger. Namaroff keeps Carla under watch, with Ratoff following, while the full moon rises. Paul visits the graveyard and digs up Jules’s body, only to find it solidly turned to stone. Carla watches him in silence; she confides later that Namaroff loves her and that she fears his power. Paul promises to take her away once Megeara is defeated, though she fears it may be too late.
Meister arrives at the millhouse to support Paul. Meanwhile, Martha dies soon after recapture by Ratoff. Meister and Paul seek Inspector Kanof [Patrick Troughton], pressing him to reveal Carla’s arrival in Vandorf as an amnesiac prior to the first murder.
In a secret meeting at Castle Borski the next morning, Carla tells Paul that she will flee with him, but he refuses and she runs off. Paul gives chase and is attacked by a waiting Ratoff, who is deterred by Meister. Meister surmises that Carla becomes amnesiac during the full moon, a period during which Megeara’s spirit may inhabit her body. Paul agrees that Carla must leave immediately, with him intending to follow later once the mystery is solved. He later sends a cable to Leipzig about Carla’s supposed arrival by train, but there is no trace of her.
That night, Paul returns to Castle Borski as the full moon climbs. In the ruins, Namaroff awaits Carla’s arrival with a sword. The two fight while Megeara materializes. Namaroff attempts to behead Megeara, but his own view of her face petrifies him. With Namaroff’s sword, Meister beheads Megeara, yet the act comes too late to save Paul, who has already seen Megeara’s face. As he slowly turns to stone, Paul gazes upon Megeara’s severed head, which morphs into Carla’s visage, sealing the transformation and the tragedy.
The tale unfolds as a haunting clash between mortal doubt and an ancient, stone-cold myth, with love, loyalty, and a doomed fate intertwining in Vandorf’s haunted landscape.
