A tough teacher with an attitude and her cute student have an exciting time at school. Na Bo-Ri(Kong Hyo-Jin) was a legend in high school for being a troublemaker and getting into fights. Then one day she gets expelled from school for being involved in a fight. After overcoming numerous hardships, she gets a job as a substitute teacher at her old high school. She is excited with the fact that she will be able to meet her old teacher, Ji Hyeon-Woo(Kim Da-Hyun), whom she has had a crush on for years. But a womanizing troublemaker in her class, Park Tae-In(Gong Yoo), keeps getting her into trouble. Tae-In is a smart and an athletic student. From Tae-In’s point of view, he dislikes Bo-Ri because she isn’t smart, but at the same time, has a headstrong personality. As his relationship with his teacher turns for the worst, he gradually becomes attracted to her through a series of complicated events...