The drama follows a group of highly trained profilers in the fictional National Criminal Investigation (NCI) team who track down criminals to solve cases. It begins a year after a crucial error results in a bomb detonating at a hospital, killing several SWAT officers and leaving the NCI team leader Kang Ki Hyung's confidence badly shaken. He returns to work after a long break and is immediately drawn into a serial murder case which requires the NCI team to collaborate with the local police agency's Violent Crimes Unit. They meet the temperamental police officer Kim Hyun Joon, who appears to have a bitter grudge against Ki Hyung.