Lee Dong-Sik (Shin Ha-Kyun) was once a capable detective. He now works at the Manyang Police Substation in a small city and does all the tedious chores at the station. His life is quiet there. One day, Detective Han Joo-Won (Yeo Jin-Goo) is transferred to the same police substation. He is assigned to work as Lee Dong-Sik’s boss and also his partner. Han Joo-Won is an elite detective and comes from a distinguished background. His father has a good chance of becoming the next chief at the National Police Agency. Han Joo-Won also has a secret. A serial murder case takes place in the small, peaceful city. The case is the same serial murder case that took place 20 years ago and changed Lee Dong-Sik’s life. The two detectives work to catch the killer.