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. South Korean Intelligence soon discover Myung-hoon’s activities and begin tracking him, all the while his own government sends a vicious assassin to eliminate him.
Dongchul, who is managing a small bar, is always enthusiastic about his school reunions. One day, Yujin, who has never showed up to a reunion, shows up at his bar. Her baby face and vitality make her unlike other married women and all the men fall for her, especially Dongchul. They start a relationship but it abruptly flames out due to the sudden arrival of Dongchul’s wife. As they get to know each other's secrets, will their love be allowed to grow?
Sung-hyeon reunites with first love, Jin-hye at a class reunion.