Na Bo-ri (
Gong Hyo-jin) is a 25-year-old woman who desperately wants to be a teacher at the high school she was kicked out of due to a misunderstanding with her teachers over injuring a group of male classmates (she had been a legend there for being a troublemaker and getting into fights). After overcoming numerous hardships and getting her high-school equivalency certification, she rejects job offers from other high schools and works on becoming a substitute teacher at her old high school so she can work side by side with her longtime high school crush, the art teacher Ji Hyun-woo (
Kim Da-hyun). However, the only thing that enables her to get the coveted job is by signing a contract to essentially babysit Park Tae-in (
Gong Yoo), a troublemaker who attends the same high school. Tae-in, a lonely 20-year-old youth, quickly becomes the "jjang", or "king" of the high school, and enjoys playing mean tricks on Bo-ri whose tough but easygoing personality attracts the majority of her students. As his relationship with his teacher takes a turn for the worse, Tae-in gradually becomes attracted to her through a series of complicated events. Noh Jem-ma (
Choi Yeo-jin) is jealous of the relationship between Bo-ri and Tae-in, and goes out of her way to get Bo-ri kicked out but she's not the only one against them. ==Cast==