On the first day of the new elementary school year in Korea, Ms. Yeo Mi-ok lays down the law to her students. She is strict and demanding. When her new student Go Mi-nam arrives late and calmly takes her seat, Yeo ignores Mi-nam. Assigned bathroom cleaning duty as punishment, Mi-nam beats up the girls who taunt her and forces them to clean instead. At home we see that Mi-nam lives with her mother, who rarely has time for her because of the hours she must work at the food and alcohol tent she owns.
Back at school, the newest male teacher Mr. Kwon Sang-min is causing a stir with his handsome good looks, and every female teacher and student is falling for him. Mi-nam tries to apologize and unburden herself to Ms. Yeo, who ignores her while trying to impress Mr. Kwon. Mi-nam decides to compete for him as well, even getting his cellphone number. Mr. Kwon goes to Ms. Yeo for advice on how to deal with the students' affection, not realizing she likes him too. The teacher and the student start a heated rivalry that climaxes when Ms. Yeo slaps Mi-nam in class—and is recorded doing so on a student's cellphone camera.
She resigns from the school but eventually makes amends with Mi-nam and returns to teach.
