Major crimes unit detective Seong-jin arrests Tae-sung for petty crimes, but shocked to find out that he is the notorious serial killer. However, Seong-jin becomes doubtful of his identity as the serial murder case is investigated.

While his girlfriend is away on a trip, retired assassin Bang Ui-kang is tasked with looking after her friend's 17-year-old daughter. After a street attack, Bang Ui-kang becomes embroiled in a murder investigation and dangerous trafficking gang.