The Killing Vote follows a mysterious figure known as 'Gae-tal' (Dog Mask) who initiates a nationwide mobile voting system to decide whether heinous criminals who have escaped the law should receive the death penalty. If more than 50% of the public votes in favor of execution, Gae-tal carries out the sentence, sparking a massive social debate about justice, vigilantism, and the failures of the legal system. The series centers on the cat-and-mouse game between the vigilante and a dedicated task force, including Kim Moo-chan, a ruthless police team leader, and Joo-hyun, a brilliant cyber investigation officer. As the death penalty votes continue, the protagonists must navigate the moral ambiguity of the situation while uncovering the identity of the masked executioner and the dark secrets behind the system itself.