After his father, a North Korean spy, fails a mission and is accused of treason, Myung-hoon and his younger sister Hye-in are sent to a labor camp. In order to save his sister and redeem his family's honor, Myung-hoon agrees to become a spy himself. He is sent to South Korea, posing as a defector while attending high school. There, he meets Hye-in, a bullied girl of the same name as his sister, and becomes entangled in her plight while trying to fulfill his mission.

As Myung-hoon navigates his dual life, he is constantly watched by both North Korean operatives who distrust him and South Korean agents who suspect his true identity. Performing covert missions ordered by his superiors, he finds his determination strained by moral dilemmas and the growing bond with the South Korean Hye-in. Survival becomes increasingly uncertain as loyalty, betrayal, and survival clash, pulling Myung-hoon deeper into a labyrinthine power struggle.