Doctor Gerald Antrobus runs an Asylum for the criminally insane. One of his patients, the 120 year old Professor Rex Sheppard, tells Antrobus that his pet demon-dog has told him of an unspeakable evil that awaits the doctor. Antrobus receives a letter from the wheelchair bound General Lord Waverley, telling him that his dead father, who he didn't know he had, has left him an estate in his will. On arriving in a strange village, in a desolate part of Cornwall, he discovers almost everyone is dead, killed by a rampaging monster called Miasma, which happens to be a demon, inhabiting the dead corpse of his mother - who he also didn't know he had. Miasma had cheated on his father with the General, who then jilted her for a vampire. She then ran off with the aforesaid professor whose demon dog bit her, causing her death - which she then arose from as the before mentioned rampaging monster, bent on the General's destruction. Can Antrobus destroy this terrible creature, who kills with her own