Although Sujin and Suyeon are sisters, their personalities are completely different. Su-jin is honest and loves sex, while Su-yeon is shy and not sexually open. Sujin quit her job and is enjoying free sex with her boyfriend Kyungho. Because Sujin is too revealing, Kyungho is burdened with having sex with Sujin. Su-yeon is dating her co-worker Min-hyuk, but while her father is on a business trip, Su-yeon and Su-yeon invite their boyfriends to their house, have a drink together, have a good time, and go to bed, but go to the bathroom. Min-hyeok, who was looking for him, sees Su-jin’s masturbation during Su-jin’s visit, and Kyung-ho goes to the bathroom, misunderstood Su-yeon’s room for Su-jin’s, enters, and lies down next to Soo-yeon… That night, something unexpected happened to the sisters.