Before he becomes the famed horror writer H. P. Lovecraft, young Howard Lovecraft is a curious and imaginative boy living with his mother, because his father is locked up in Arkham Sanitarium. But after his mother unwittingly gave Howard the legendary Necronomicon, Howard went to a dangerous and frozen land where he saved and befriended a monstrous creature he named Spot. Howard thought that was behind him, but now there is a new threat, and only Howard and Spot can save the day. Howard’s mother has been kidnapped and evil forces are turning Howard into a fish creature.

A vengeful witch and her fiendish servant return from the grave and begin a bloody campaign to possess the body of the witch's beautiful look-alike descendant. Only the girl's brother and a handsome doctor stand in her way. Barbara Steele stars in Mario Bava's directorial debut. Black Sunday was considered unusually gruesome, and was banned in the UK until 1968 because of its violence. In the US, some of the gore was censored in-house by distributor American International Pictures before its theatrical release.