When Kang Bok-Soo was a high school student, he was falsely accused of committing violence and kicked out of school. 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.

Ki Moo-Hyeok, a lawyer with a high winning rate, only cares about money. Due to a murder case at a high school which he deals with, his reputation as a lawyer hits rock bottom. To regain his good name as a lawyer, he sneaks into the high school and work as a temporary teacher. He tries to reveal a secret which the students have, and gets involved with Teacher Ha So-Hyun, a P.E. teacher who loves her students. They then face the students'secret.

South Korean drama based on the American television series Criminal Minds. Profilers investigate cases from the perspective of the criminals to solve them.