Count Carl von Bruno's efforts to establish a personal empire in Africa have been thwarted by three Englishmen. As he departs in defeat, a mysterious Portuguese merchant offers to sell him a strange Creature captured in the jungles of South America. Von Bruno acquires the Creature and returns to his home, The Black Castle in Austria. There he plans to use the inhuman beast as part of his revenge on the three Englishmen who thwarted him.
Von Bruno does not count on the Creature escaping from its confinement, nor does he anticipate the unnatural attraction it has formed for his beautiful but strange fiance.
What ensues is a desperate monster hunt through the passages under the Black Castle and the surrounding countryside, ending ultimately in a fatal showdown.