Yoon Ji-woo is the daughter of Yoon Dong-hoon, a gangster. On the night of her seventeenth birthday, Ji-woo witnesses her father's getting shot to death by a hooded man. As the police are unable to find the killer, Ji-woo asks for help from Choi Mu-jin: Dong-hoon's boss and close friend, and the leader of Dongcheon, an organized crime syndicate. Although reluctant at first, Mu-jin takes Ji-woo under his wing, encouraging her to become strong enough to get her revenge. He places her in his fight training gym with other gang recruits and personally gives her hand-to-hand training.