The son of a North Korean spy decides to follow in his father's footsteps to protect his little sister. After his father's botched espionage mission, North Korean Myung-hoon and his young sister Hye-in are sent to a labor prison camp. In order to save his sister's life, Myung-hoon volunteers to become a spy and infiltrates the South as a teenage defector. While attending high school in the South, he meets another girl named Hye-in, and rescues her when she comes under attack.