Kyung-chul is a dangerous psychopath who kills for pleasure. Soo-hyeon, a top-secret agent, decides to track down the murderer himself. He promises himself that he will do everything in his power to take vengeance against the killer, even if it means that he must become a monster himself.

Eun Guk and Eun Soo are siblings living alone after their father passed away. Eun Guk works at the post office. He feels like he is getting older, because of his younger sister's behavior like skipping school to attend an audition. Meanwhile, Eun Soo thinks her life is weary even though she is only 10-years-old. She thinks that because of her older brother, she can't pursue her dreams. Eun Soo then decides to leave for Seoul to achieve her dreams. One day, their mother appears in front of them.