When Hong Ji-won realizes that her precious son Hae-sung has leukemia, she swears that she will sell her soul to devil if she could save her son. An ambitious and smart high school girl Yeo-ri is adopted by the CEO of With Group when her father, a driver of With Group’s CEO, dies from a car accident. However, when Ji-won finds out that Yeo-ri’s bone marrow matches that of Hae-sung, she asks her to undergo a bone marrow transplant surgery. However, pregnant with her boyfriend’s baby, Yeo-ri decides to leave the house and erase her identity to escape the grip of Ji-won.