Joan Collins' home in this movie is the exact same home as Patrick McGoohan, as seen in opening credits of every episode of his "The Prisoner" TV show.
The Carlesis' car is a 1972 Fiat 124 Sport Coupe. Tommy's red car is a 1974 Ford Capri GT MkII.
This movie is also known as "The Devil Within Her"
Donald Pleasence began filming immediately after arriving back from Hollywood where he'd just finished shooting Hearts of the West (1975).