The son of a North Korean operative chooses to follow his father’s path to safeguard his younger sister. After his father’s espionage mission goes awry, Myung-hoon and his sister Hye-in are sent to a labor camp in North Korea. To ensure his sister’s survival, Myung-hoon offers to become a spy and infiltrates South Korea, posing as a teenage defector. While attending high school there, he encounters another girl named Hye-in and saves her from an attack. Meanwhile, South Korean Intelligence becomes aware of Myung-hoon’s actions and starts monitoring him, as his own government dispatches a ruthless assassin to take him out.