Yoon Ji-Woo’s (Han So-Hee) father dies suddenly. She wants to desperately take revenge on whoever is responsible for her father's death. Yoon Ji-Woo works for drug crime group Dongcheonpa.Choi Mu-Jin (Park Hee-Soon) is the boss of the drug gang. With the help of Choi Mu-Jin and to uncover the reason for her father's death, Yoon Ji-Woo joins the police department and becomes a mole for the drug group. Yoon Ji-Woo is assigned to work in the drug investigation unit in the police department. Her partner there is Detective Jeon Pil-Do (Ahn Bo-Hyun).