Ace NIS agent Jung Hae-seong is demoted after a mission failure. He goes undercover at a high school to locate King Gojong's missing gold, meeting his teacher Oh Soo-ah, who sees him as her lost first love, stirring old heartbreak.

A high school student with amnesia tries to uncover what has happened to her. All leading her into deeper troubles ultimately revealing a darkness she could not have imagined.