The story about a woman who joins an organized crime ring and infiltrates the police as an undercover agent in order to find out the truth about her father's death.

Yoon Ji-woo's 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 Moo-jin is the boss of the drug gang. With the help of Choi Moo-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.