The seventeenth birthday of the high-school senior Yunji-u did not go well. Not only because of her father's criminal activities are the police tailing her, her classmates harass her, and the teachers are ready to transfer the troublesome student to another school; moreover, the father, a gangster, had not been home for a long time. When he finally comes to see his daughter, he is killed in front of her eyes, right at the apartment entrance. Torn by guilt and hatred, Yunji-u asks for help from her father's criminal partner, boss Choi Mu-jin. He, convinced that the murder was committed by a police officer, decides to give the girl a chance to take revenge—sends her to train with young gangsters, and later gives her a fake name and embeds her into the police ranks.