年青考古学家安格斯。在女朋友玛莉住的美斯农场附近，发掘了一个类似蛇的头骨，没多久，玛莉的父母失了踪，而住在村里的神秘女士西维亚，又从外面回来，她是蛇妖的化身，捉了玛莉的妹妹依芙，准备将她奉献给蛇妖。举行奉献仪式时，安格斯及时赶到，与蛇妖展开了一场决斗。Scottish archaelogist Angus Flint discovers an odd skull amid the ruins of a convent which 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 lands, right next to Temple House. Angus learns of the D'Ampton Worm, a huge dragon/snake which an earlier D'Ampton killed by cutting it in half. (There's a pretty catchy rock-folk song that tells the D'Ampton Worm legend.) As people begin disappearing and acting strangely over the next day or two, the skull is stolen from Angus' room, and the watch of a missing person is found in a cavern which was the legendary home of the D'Ampton worm. Angus and James discover that there was an ancient cult which worshiped the worm as a god, and theorize that the creature somehow survived its "destruction", but was trapped inside the cavern. The remainder of the movie shows Angus, James, and Mary Trent attempting to stop Lady Marsh from freeing the creature...