CURSE OF THE DEMON

In England, Professor Harrington begs his rival, Dr. Julian Karswell, to rescind a curse he inflicted on him; in return, Harrington will cease his investigation into Karswell's Satanic cult. After learning that a parchment he gave Harrington has been destroyed, Karswell merely promises to do what he can. As Harrington arrives home, he sees a cloud of smoke appear out of nowhere and a gigantic demon materialise from it. Harrington tries to escape in his car but crashes into power lines. The authorities declare accidental electrocution as the cause of death.

Dr. John Holden arrives in Britain to attend a convention at which Harrington had intended to expose Karswell's cult. He is informed that the only link between Harrington's death and Karswell's cult is a man suspected of murder, Rand Hobart, who has fallen into a catatonic stupor. While Harrington's collaborators consider the possibility of supernatural forces, Holden rejects such an option.

Holden meets Karswell apparently by chance at the British Museum Reading Room. When a rare book that Holden requests goes missing, Karswell offers to show Holden his own copy at his mansion. At Harrington's funeral, Holden meets Harrington's niece, Joanna. She gives him Harrington's diary, which details Harrington's fear of Karswell's power. Holden remains sceptical, but goes with Joanna to Karswell's mansion the next day, where Karswell is holding a Halloween party for local children. When a strong windstorm abruptly starts, Karswell claims to have created it with a spell. When Holden mocks him, Karswell claims that Holden will die in three days.

Holden and his colleagues discuss Karswell and make plans to examine Rand Hobart. Holden goes to dinner with Joanna and she shows him her uncle's diary. Harrington's diary mentions a parchment with runic writing on it that was passed to him by Karswell, and Holden finds a similar parchment that Karswell secretly passed to him at the library. A powerful wind comes through the window, blowing the parchment from his fingers towards the fireplace, only to be stopped by a fire screen. Holden recovers and pockets it.

Holden visits Hobart's family to seek permission to hypnotise Hobart and find out about the death he is suspected of. The mother gives her consent but says that the family are "believers". As Holden leaves, the parchment is blown from his hand. Hobart's family becomes fearful and declares Holden to be "chosen". Later, Holden compares the parchment's runes to ones inscribed on the nearby stone circle at Stonehenge.

Joanna takes Holden to a séance at the invitation of Karswell's mother. A medium claims to channel Harrington, who tells them that Karswell has the key to reading the runes in his copy of the rare book. After Holden abruptly exits, dismissing the séance as nonsense, Joanna says she intends to search for the key and they drive to Karswell's mansion. Holden breaks into the house while she waits outside. Inside, he is attacked by a cat that seems to morph into a panther. Holden is rescued by Karswell entering and switching on the light, saying he knew Holden would come. Against Karswell's warning, Holden leaves through the woods, and believes he is chased by a cloud of smoke and fire before escaping.

Under hypnosis, the suspect Hobart reveals to Holden that he was "chosen" to die by having a runic parchment passed to him, but avoided death by passing it back to the person who had given it to him. When Holden shows Hobart the parchment he had received from Karswell, Hobart thinks he is trying to give it to him. He becomes hysterical and jumps through a window to his death.

Holden learns Karswell is taking a train to Southampton, and on the train discovers that he has kidnapped and hypnotised Joanna. As the time for Holden's predicted death draws near, the train stops at the next station, and Karswell tries to leave. Holden manages to sneak the parchment into Karswell's coat pocket, and when Karswell finds it, it flies from his hand. He chases it down the tracks, but as he reaches it the parchment combusts. As an oncoming train approaches, the demon manifests and attacks Karswell. When his corpse is found by the tracks, the police believe that he was struck and dragged by the train. Holden, instead of going to inspect the body, departs with Joanna.

Karswell is killed by the same demon he summoned after the cursed parchment is returned to him, ending the supernatural threat.

The film concludes with skeptical Dr. Holden managing to pass the cursed runic parchment back to Karswell, forcing the occultist to face the consequences of his own diabolic pact. The demon appears and kills Karswell, affirming the reality of supernatural forces while punishing their misuse. Holden’s rational worldview is shaken, suggesting that some phenomena defy logical explanation.