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 |
| Camera | Ken Hodges | Director of Photography |
| Writing | August Derleth | Book |
| Costume & Make-Up | Caroline Mott | Costume Design |
| Writing | H.P. Lovecraft | Book |
| Writing | D.B. Ledrov | Writer |
| Writing | Nat Tanchuck | Writer |
| Camera | Herbert Smith | Camera Operator |
| Production | Alexander Jacobs | Associate Producer |
| Sound | Don Challis | Sound Editor |
| Costume & Make-Up | Harry Frampton | Makeup Artist |
| Art | Brian Eatwell | Art Direction |
| Sound | Kevin Sutton | Sound Mixer |
| Editing | Brian Smedley-Aston | Editor |
| Sound | Basil Kirchin | Original Music Composer |
| Production | Frederick Yale | Casting |
| Sound | Jack Harding | Original Music Composer |
| Production | Bernard Schwartz | Executive Producer |
| Costume & Make-Up | Eileen Warwick | Hairdresser |
| Costume & Make-Up | Hylan Booker | Costume Designer |
| Production | Phillip Hazleton | Producer |
