I don't know why they had to have John Saxon play the leading role in this movie; the Production Team could have chosen one of several dozen British actors who would have done a better job and better fitted the role. But then perhaps the film had American backers and they were calling the tune. Speaking of tune, the introductory song/music on the DVD version of the film is pathetic and totally incomparable to the original brilliant 60s pop instrumental "Image" with its Telstar-type organ backing. All that aside the movie is one that joins many other British SF films in the ranks of fame and is not totally unfaithful to Frank Crisp's 1963 novel "The Night Callers" on which it was based. It has moments which are slightly unnerving, particularly when the proposed candidates for shipping back to Ganymede are being interviewed by the man (monster) behind the shadows. Generally speaking there were very few dull moments and the pace of the plot was just right. Perhaps the ending could have been extended and more seen of the hideous alien with the claw-like appendages. Denham shines out above anyone else in the male cast leaving Saxon looking on from the sidelines as if he were a last minute, and not totally comfortable sub. A must see gem of a movie and despite the absence of the original introductory music the DVD will make a good addition to any SF Movie Buff's collection.