After a failed mission, an NIS agent must go undercover at an elite high school with his team to recover $80M in gold bars. To save his career, Hae Seong dons a school uniform for this unlikely assignment.
Hae Seong nearly reveals himself while hunting for gold in the school's old building. Evading teacher Su A, he faces bullies and tight security as he plans his next search amid disturbing rumors.
Hae Seong uncovers a crucial clue hidden within the old building, but Chairwoman Seo quickly learns its potential connection to the elusive gold bars. Sensing the connection, she keeps Hae Seong under close watch.
Hae Seong attends the anti-bullying committee session with a key witness who clears his name, while Dong Min finally finds the courage to stand up for himself.
Hae Seong and the team grow increasingly concerned that Su A's suspicions could threaten his undercover mission. However, Hae Seong defies the odds and successfully gains a spot in the student council.
The school's security guard dies, leaving Hae Seong a notebook belonging to his missing father. The revelation is shocking, and he storms the NIS for answers. The answer pushes him away from the mission, and he takes time off.
After uncovering the possibility of a mole within the NIS, Hae Seong becomes increasingly distrustful of those around him, causing him to question the mission's integrity.
The gold bars vanish just as they are within reach, and Seo Myeong Ju suspects Hae Seong has them. In the vault, Hae Seong makes a heartbreaking discovery of his father's remains.
Despite getting badly injured, Hae Seong manages to call Su A and his team. They conclude that the only evidence they can secure is the flash drive that contains the voice recording of Principal Park murdering Director Kim Hyung Bae.
