An architect and his wife are staying in an empty castle in California. They are joined by an unhappily married lawyer and his wife. Things start getting strange when they spot a half man/half beast prowling around the house and keep seeing a headless woman wandering the grounds.

A rich but unscrupulous old woman plots with a scientist to have her brain implanted in the skull of a sexy young woman.

In 1880, Sir Robert Cargrave, a London physician known for his experimental work in paralysis treatment, is summoned to Gorslava by the mysterious Baron Sardonicus—who is now married to Cargrave's former wife, Maude—to treat his disfigurement. When Cargrave arrives, he finds the masked baron is a cruel sadist who has threatened to harm Maude if he is not successfully cured.