I just saw this thing on TV and quickly came to the conclusion that Stephen Boyd was in it simply to give him a job.Ditto Diana Dors and Christopher Lee.I'm sure they had worked out of this [UK]studio before.If I remember correctly this was a rough time for Hollywood and a lot of actors were working wherever they could to make ends meet.
shareMore like they loaded this film with name actors to support Rachel Welch. She was pretty much a just for show sex symbol and not expected to carry a dramatic film like this.
shareStephen Boyd wasn't a star very long(his villainous turn in 1959's Ben-Hur did it for him) but he was a second-tier star in 1966 when he made a movie with the "new" Raquel Welch called "Fantastic Voyage" -- the one where people and a submarine are miniaturized to explore the human body.
Perhaps Boyd did this as a favor to his old co-star.
Boyd's career was flopping by this point, and he died fairly young of heart attack about 6 years later. Milton Berle claimed that Boyd, whom he didn't know at all, died in his arms as they were passing each other at a country club where Boyd had just finished a round of golf...