The story takes place in a boys' high school, where Hyo-joo (Kim Ha-neul) has been working as a contract worker for many years. This means that no matter how good her performance is or how strong her ability is, she may be fired at any time. Hyo-joo has an extreme desire to enter the system. However, a new female teacher named Hye-young (Yoo In-young) has recently arrived in the school. Not long after she arrived, Hyo-joo got a full-time job. The reason is very simple. Hye-young is the daughter of the school's chairman. Hyo-joo is very angry about Hye-young's regular job. By chance, Hyo-joo learns that Hye-young has an ambiguous relationship with a boy named Jae-ha (Lee Won-geun) in her class. This becomes Hyo-joo's trump card to conquer Hye-young. Hyo-joo vows to take everything from Hye-young, including Jae-ha.