Yoo-jeong and So-hyeon are not real siblings but have lived together since childhood. So-hyeon is caught by Yoo-jeong spending time at home with her boyfriend. Min-soo saw Yoo-jeong naked in the bathroom. Yoo-jeong is interested in such Min-soo and seduces Min-soo. Min-soo knows that Yoo-jeong and So-hyun are not real sisters and approaches Yoo-jeong right away. So-hyeon finds out and So-hyeon breaks up with Min-soo. Min-soo played with two sisters...