After a successful night of partner-swapping, Alan and Wendy feel their spark has returned and decide to go back to their normal, monogamous life.

Jack and Louise Bauer are a suburban married couple whose sex life has grown stagnant. Seeking excitement, they join an underground swingers club called the . There they meet another couple, Hank and Wendy Barnet. An exchange of partners begins, but soon jealousy, obsession, and manipulation surface. Wendy becomes fixated on Jack, while Hank crosses emotional boundaries with Louise. The film builds toward a violent and paranoid climax as trust disintegrates.

They meet Jack and Louise Bauer, an experienced swinger couple.