The son of a North Korean spy decides to follow in his dad's footsteps to safeguard his sister. After his father's botched espionage assignment, his sister Hye-in along with North Korean Myung-hoon have been sent to a labour prison camp. As a way to save his sister's lifetime, Myung-hoon infiltrates that the South and volunteers to become a spy. He rescues her as she's under attack, and meets with another girl called Hye-in while attending high school in the South. The activities of Myung-hoon are so on discovered by south Korean Intelligence and start tracking him , all of the while their government sends a vicious assassin to eradicate him.