After his father's failed espionage obligation and disgraced death, North Korean Myung-hoon and his young sister Hye-in are sent to a labor prison camp. In order to protect his sister, Myung-hoon agrees to become a spy and penetrates the South to accomplished his father's undone mission. While attending high school in the South, he makes friends with a girls also named Hye-in, and rescues her from bully fellows. South Korean Intelligence soon discover Myung-hoon's activities and start hunting him, while his own government also sends a savage assassin to eliminate him.