The murder of her sister sets Su Yeon out for vengeance. While she works with Chang Chun Woo, a black agent working undercover in the Samhwa Gang, the man she was after appears in a drug deal. Her desire for revenge overtakes her and puts the operation in jeopardy.

Su Yeon rushes to the site where the deal is happening to help Chun Woo, who is at risk of being exposed. Meanwhile, Chun Woo does whatever he can to prove his innocence and keep the situation under control when word of a possible rat surfaces. However, all fingers point to him being the rat, making things frustrating and dire.