When a series of terrible murders ensues in a residential area, Cha Su-yeol is forced to seek help from Jung I-shin, a serial killer from the past.

The culprit has been arrested, but the victim's whereabouts remain unknown. Su-yeol struggles to save a life as I-shin reveals her true intentions.

I-shin offers assistance with the investigation, but it's unclear why she would help a cop. Su-yeol unravels the origins of I-shin's murderous instinct.