This nocturnal tale of horror begins when Robert Manning (Mark Eden) takes refuge for the night in Greymarsh Lodge while searching for his missing brother. The antique dealer is fascinated by the collection of ancient torture equipment owned by his host Professor Marsh (Boris Karloff). The professor is an expert in witchcraft, and Morley (Christopher Lee) is his macabre assistant. Morley is the descendant of a witch burned at the stake by an ancestor of Robert. Morley spikes Robert's brandy with a hallucinogenic drug and sets out to seek revenge for the death of his ancestor 300 years ago.