This was Joan Fontaine's final film, perhaps due to its poor box office reception, though she continued to work consistently in television well into the 1980s (one final project came in 1994).
Joan Fontaine reportedly purchased the film rights to Norah Lofts' novel (written under the nom-de-plume of Peter Curtis) and brought the project to Hammer.
In a later magazine interview, Nigel Kneale said that he was dissatisfied with the way the film had turned out. Personally, he found modern black magic practitioners to be fairly risible and he had intended to poke fun at the idea of an English coven. His blackly comic touches were removed by the production team, who wanted the film to be entirely serious. Conceding the film to be well-cast, he felt the ending lacked the necessary menace needed to avoid the unintentional-but-inherent silliness of the situation.
This would be the final film performance for former child star Martin Stephens before his retirement from the film industry.
Based on the novel 'The Devil's Own' by Norah Lofts, under the pen name of Peter Curtis, it was released in America under that title.