Scottish archaeologist Angus Flint discovers an odd skull amid the ruins of a convent that he is excavating. Shortly thereafter, Lady Sylvia Marsh returns to Temple House, a nearby mansion, far earlier than expected. At a party in the village, Angus meets Lord James D'Ampton, who has just inherited his family's land right next to Temple House. Angus learns of the D'Ampton Worm, a huge dragon-snake that an earlier D'Ampton killed by cutting it in half. (A catchy rock-folk song that tells the D'Ampton Worm legend.) As people begin acting strangely and disappearing over the next few days, the skull is stolen from Angus's room, and a missing person's watch is found in a cavern that was the legendary home of the D'Ampton worm. Angus and James discover that an ancient cult worshiped the worm as a god, and they theorize that the creature somehow survived its destruction, but was trapped inside the cavern. The rest of the film shows Angus, James, and Mary Trent attempting to stop Lady Marsh from freeing the creature..