NIS agent Jung Hae-Seong, undercover as a student at Byeongmun High School, faces escalating challenges. His homeroom teacher, Oh Soo-A, grows suspicious of his frequent absences, jeopardizing his covert mission to locate Emperor Gojong's missing gold bars. Simultaneously, Hae-Seong discovers his cousin, An Yu-Jeong, is being bullied, adding personal stakes to his assignment.