Three In The Attic (1968)

aka: 3 In The Attic

In the swinging 60's three girls (Yvette Mimieux, Judy Pace and Maggie Thrett) discover they have the same boyfriend (Christopher Jones) who has been playing around with them all while vowing fidelity to each. To teach him a lesson he won't forget, the trio contrive to lock him up and continually favor him with their attentions in turn. Also with John Beck.