Couples Bob & Carol Sanders and Ted & Alice Henderson are best friends. After attending a weekend self-help self-discovery session (Bob is planning on making a documentary film on the subject), Bob and Carol feel newly enlightened, and want their friends, Ted and Alice, to feel the same way. "Feel" is the operative word as they want people now to feel rather than think. The foursome each examine their feelings, and admittedly their thoughts toward their individual relationships with each other and the topic of sex when Bob admits to Carol that he had a meaningless sexual dalliance, which Carol later mentions to Ted and Alice. After pushing the sexual boundaries with others, the foursome decide they have one last boundary to cross truly to test what they consider their new enlightened state.