Sehun's father had been killed by a batch of gangster. Luckily he is alive. After his father's death, he stay with Mr. Daniel Henny, his father's bestfriend which also works as Special Agent of Korean Crime Investigation(KCI). Sehun wants to get revenge for his father's death but Mr.Daniel told him to be patient because they still don't know who was responsible for the murder. Sehun had been recruited as SA for his skills and he completed all of his task with excellent achievement but one day, he get a task to investigate about Mr. Lee Deok Hwa. In order to do that, he try to become close with Lee Yoona, Mr Lee's daughter.