Carl and Diana are a cynically open, libertine couple who proudly reject traditional relationship boundaries. By contrast, Adam and Béatrice are disciplined, structured, and committed to total marital fidelity—at least in theory. When the two couples cross paths at a party, sexual tension and curiosity quickly destabilize their long-held beliefs, causing their partnerships to swap and forcing all four to re-examine their views on love, desire, and monogamy.