Be sure to see the 'Making of' documentary "To the Devil... The Death of Hammer"

This was Hammer Films' last horror movie and penultimate film. While financially successful at the box office, likely due to the shocking bits (e.g. a tacked-on obscene "devil baby" sequence) and nudity (e.g. a satanic orgy that is more silly than anything else), it doesn't make up for a flat story with a tepid close.

The DVD includes an informative and entertaining 24-minute "making-of" documentary that discusses the film and the demise of Hammer Studios, which features interviews with Lee, Blackman, the director, the producer and many more.

By all accounts Richard Widmark was arrogant and a real bastage to work with. The Hollywood "star" frequently insulted the English filmmakers (calling the picture a "Micky Mouse production"), walking off the set, arguing, brawling and kicking over expensive equipment (!). Every aspect of the movie is addressed, including changes from the novel, Dennis Wheatley's objections, the last act's failure, etc.

Needless to say, the documentary is more entertaining than the film itself and is available on Youtube here: https://www.youtube.com/watch?v=HDNiW9VtS4g