A tragic affair destroyed the lives of Do Chi-kwang (Han Suk-kyu), Kim Yeong-goon (Seo Kang-joon) and Han Tae-joo (Kim Hyun-joo). The three join forces and become members of an internal affairs investigation team for the police and try to dig up the truth on who is behind the tragic affair.
Do Chi-Kwang is an elite detective. He is thoughtful and smart. He is proud of his track record of catching criminals. He realizes the importance of work done by the police on corruption and becomes the chief of the internal affairs investigation team.
Kim Yeong-goon is a police officer and member of the mobile patrol team. He acts cold to other people, but is actually tender persona with a warm personality. By accident, he happens to meet Do Chi-kwang. Do Chi-kwang got involved in a the tragic affair, which Kim Yeong-goon tries to forget. To find the truth behind that case, he joins the internal affairs investigation team.
Han Tae-joo is a popular lawyer. She worked as a prosecutor previously. She became entangled in a case unexpectedly and survived even though her life was in grave danger. She then quit her job as a prosecutor and became a lawyer. She meets Do Chi-kwang and Yeong-goon and joins their internal affairs investigation team.