Layar-21 – Hyuk and Kyung have their share of marital problems, one of them being a stagnating sex life. Kyung again rejects Hyuk’s advances and Hyuk goes to bed feeling hurt and angry. The next morning, the couple discuss their problems and decide to take a romantic weekend trip to add fire to their marriage. But when Hyuk fails to perform, they are back to square one. The following Monday, Hyuk confesses his story to his colleague Woo. Woo suggests swapping partners by joining a secret club called Club Butterfly . Hyuk soon receives a mysterious email from an anonymous sender urging him to join this illicit club. Neither Hyuk nor Kyung knows what is in store for them.