When Kang Bok-soo gets wrongly expelled from a school in his youth, he vows to return to the institution to enact revenge against the perpetrators. However, he meets someone who changes his life. This was caused by his first love Son Soo-Jung and a male student Oh Se-Ho. Kang Bok-Soo is a now an adult, but his life has not gone smoothly. To get revenge on Son Soo-Jung and Oh Se-Ho, he returns to the same high school as a student. The environment at the school has changed and Kang Bok-Soo gets involved in unexpected cases.
