In a small island off the American coast, the Whateleys live in an old mill where a mysterious bloody being creates an atmosphere of horror. After her parents get killed by lightning, young Susannah is sent to New York by her aunt Agatha, who wants her to avoid the family curse. Years later Susannah, now married, persuades her husband to spend a holiday in the abandoned mill. Once on the island, Susannah and Mike soon find themselves exposed to the hostility of a gang of thugs led by Ethan, Susannah's brutal cousin.
| Directing | David Greene | Director |
| Writing | H.P. Lovecraft | Book |
| Writing | August Derleth | Book |
| Camera | Ken Hodges | Director of Photography |
| Costume & Make-Up | Caroline Mott | Costume Design |
| Writing | D.B. Ledrov | Writer |
| Writing | Nat Tanchuck | Writer |
| Sound | Basil Kirchin | Original Music Composer |
| Sound | Jack Harding | Original Music Composer |
| Editing | Brian Smedley-Aston | Editor |
| Production | Frederick Yale | Casting |
| Art | Brian Eatwell | Art Direction |
| Costume & Make-Up | Eileen Warwick | Hairdresser |
| Costume & Make-Up | Harry Frampton | Makeup Artist |
| Production | Phillip Hazleton | Producer |
| Production | Bernard Schwartz | Executive Producer |
| Production | Alexander Jacobs | Associate Producer |
| Sound | Don Challis | Sound Editor |
| Sound | Kevin Sutton | Sound Mixer |
| Camera | Herbert Smith | Camera Operator |
| Costume & Make-Up | Hylan Booker | Costume Designer |
