Swapping, That Dangerous Sex: Jeong-hyeok happens to meet In-joo, a former karaoke helper, in his neighborhood while being bored with his married life with Eun-hye. In-joo sees Jeong-hyeok's affair and takes advantage of it and asks him for money, but Jeong-hyeok seduces her to swapping because he will give her more money. In-joo, who needed travel funds with her lover Woo-seong, allows swapping and begins to swap. Embarrassed by his lover's and husband's swapping proposal, Woo-seong and Eun-hye are forced to share the swapping. Then Woo-seong and Eun-hye are attracted to each other, and they meet secretly.