10 years ago, the protagonist Lee Si-woo lost his parents to a serial killer. He finally meets the serial killer Jack who killed his parents and beheads him... but the severed head doesn't die and speaks to him. "I wasn't the one who killed your parents." After learning that the real culprit is a "contractor" who belongs to a group of serial killers who use supernatural powers, Lee Si-woo decides to hunt down the contractors with Jack's help.