The popular Bok Su teams up with the studious Soo Jeong to improve his grades. Later, Bok Su starts developing feelings for Soo Jeong as their private lessons progress.

In 2018, Soo Jeong gets conned by her colleague and ends up paying a great deal of money to become a full-time teacher at Sulsong High School.

Bok Su dives into the river to save the woman who seems to have tried to kill herself; he's shocked to discover the woman is Soo Jeong; Young Min's revelation about Sulsong High School's education system stirs up public outrage and sparks a protest.

Mr. Park, who was Bok Su's homeroom teacher in high school, visits Bok Su and suggests that he should go back to school.

Bok Su puts his old school uniform back on and goes back to the school he dropped out almost a decade ago; old friends show up as his teachers, and even the chairman of the school board; Bok Su is assigned to the same classroom as his nephew.

After his first day back to school, Bok Su can't stop thinking about Soo Jeong and about what happened between them in the past; Soo Jeong is shocked to have Bok Su as her student; Bok Su calls Soo Jeong to the rooftop to resolve what happened.