When heinous criminals evade punishment under the law, all citizens over the age of 18 receive a text message asking whether that person should receive the death penalty. If more than 50% vote in favor of the death penalty, that person is killed by "Dog Mask," a mysterious figure operating in the virtual world. Meanwhile, the police are pursuing "Dog Mask," and three people become involved: Kim Moo Chan, chief of the First Investigation Team at the Southern Police Agency, Kwon Seok Joo, a former renowned legal scholar who killed the rapist who assaulted his young daughter and then turned himself in to the police; and Joo Hyun, a police officer who has worked for five years at the Cyber Security Bureau of the Seoul Metropolitan Police Agency.