A detective who was chasing the real culprit of a serial murder case faces the hidden secret of his family. Jin-sung is a cheerful yet nasty-tempered detective at Woojin Police Station who fights for justice with all his heart. Meanwhile, Young Ju is a competent prosecutor with a high winning rate who believes that injustice must be punished through injustice. She is also an old friend of Jin-sung and Jin-woo. Jin-sung transfers to a special investigation team in Seoul for serial murder cases and carries out the investigation with Young-ju. However, Jin-woo, Jin-sung's brother, gets arrested as a suspect of the serial murders.