Kyung and Hyuk are an ordinary thirtysomething couple with a son in kindergarten. When Hyuk wants to have sex, Kyung is too tired. They discuss their sexual problems one morning on the way to work, and decide to go on a weekend trip by themselves. However, once on the trip, Hyuk fails to feel any sexual arousal with his wife and the couple ends up more distressed than before. When Hyuk mentions the situation to his friend and boss, Woo, he suggests that the couple join him and his wife in a swapping group called "Club Butterfly." Hyuk takes Kyung to the club's cabin and they fall into a conflict of morals and sexual desire.