Score (1973)

In the mythical European city of Leisure, married couple Jack and Elvira have an ongoing bet regarding who can seduce whom. This comes up in the wake of a swinging night with a couple of tourists picked up via a newspaper ad. Elvira, a self-professed "sexual snob" has bet she can seduce newlywed Betsy, married to handsome marine biologist Eddie. If she fails by midnight, then Jack gets to seduce Eddie.