Back in the 1990s, the citizens of Seoul were gripped with a paralyzing fear after a series of brutal attacks and murders occurred. A mysterious figure dubbed ‘Red Cap’ was stalking women on the streets then killing his prey, seemingly without provocation. His habit of striking at random made it impossible for the detectives to predict his next move. At the top of their minds is what could be triggering him. Aware of the American F.B.I. and its successful use of criminal profilers to identify serial killers, the head of the Criminal Behavioral Analysis team, Gook Young Soo recruits Song Ha Young, a quiet, reserved, incredibly perceptive former detective for his team. Gook believes using this new psychological method will give the police an edge in capturing 'Red Cap' and ending his killing spree. Homicide expert Yoon Tae Goo and her officers question the value of this approach and are resistant to entering such uncharted territory. To quell their scorn they need to convince that this radical crime-fighting approach will increase their arrest rates. Does Song Ha Young have the ability to gain the trust of callous criminals while seeing through them? Is he clever enough to outwit them? But more importantly, does he possess the emotional fortitude to withstand the process?