After losing her parents and everything she owns overnight, Kang Seo-yeon spends 15 years plotting revenge as Kim Yoo-jin, the adopted daughter of her enemy, Kim Do-hyung. When his son, Lee Jae-hyun, returns home, she draws him in carefully. As their dangerous game turns into real feelings, Jae-hyun falls deeply in love and even opposes Do-hyung for her sake. But when the truth comes out, he realizes he has been a pawn all along. Will he stand by Yoo-jin or turn against her?