Jung Hae Seong, an elite NIS agent facing demotion, goes undercover at Byeongmun High School to locate King Gojong’s missing gold bars. Posing as a student, he encounters O Su A, a contract Korean history teacher with dreams of becoming a full-time faculty member. As they grow closer, Hae Seong uncovers the school's dark corruption. With the help of others, he begins his fight against the powerful forces at play.