Cheon Eun-ju, who has lived a happy house wife, becomes a murderer who kills three people overnight. She has lived such a perfect life everyone is jealous of. However, as she finds a babysitter for her children, everything starts to go wrong. Jang Seok-ryu, the babysitter, makes a smart job on any given tasks at first. However, Eun-ju gradually feels that Yoo Sang-won, her husband, becomes attracted to the babysitter Seok-ryu. Even her parents-in-law have a good feeling towards Seok-ryu who is smart and meticulous woman and finally Sang-won and Seok-ryu cross the line that they shouldn’t have crossed. Watching it helplessly, Eun-ju starts going crazy and finally….
The series tells a story of a woman who seems perfect on the outside but actually suffers from impassable inferiority complex. In front of her, another woman who has what she doesn’t have shows up and her agonizing moment begins.

Cheon Eun-ju / Cast Jo Yeo-jeong
Eun-ju is a good wife and a good mother from a wealthy family. Even after many years of hardship, she manages to keep her family. She is so eager to protect her marriage life. Nevertheless, things get worse for her as she has a new babysitter come to her house.

Jang Seok-ryu / Cast Shin Yun-ju
Seok-ryu is an attractive babysitter who is very bright and friendly. Graduating from college, she decides to work as a babysitter for three children from a wealthy couple. As she works hard, she gains their trust. But, this is not it. She is up to something.

Yoo Sang-won / Cast Kim Min-jun
Sang-won has a superior family background. He is a perfectionist. Even when he struggles to get married with Eun-ju, he manages to keep his marriage life ongoing. One day, he meets Seok-ryu. First, he thinks of her as a person who is a lot alike to him. However, as time goes by, he begins to see her as a woman.

Pyo Yeong-gyun / Cast Lee Seung-jun
Sang-won’s highschool classmate. He is rich but a single. He has enjoyed a free life but falls in love with Seok-ryu at first sight. He persistently tries to win her heart, and finally succeeds marrying her. However, after getting married, he is still a playboy dating with other women.