Do Chi Kwang is an elite detective. He is thoughtful and smart. He is also proud of his record of catching criminals. After going through a series of cases, he realizes the importance of work done by the police on corruption. Do Chi Kwang then becomes the chief of the internal affairs investigation team. Kim Young Goon is a police officer and member of the mobile patrol team. He acts cold to other people, but he is actually tender with a warm personality. He does not associate with other people. By accident, he happens to meet Do Chi Kwang. Do Chi Kwang got involve in a the tragic affair, which Kim Young 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. In her past, she worked as a prosecutor. 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 Kim Young Goon and joins their internal affairs team.