The Killing Vote follows a mysterious figure known as 'Gaetal' who initiates a nationwide mobile voting system to decide whether heinous criminals who have escaped the reach of the law deserve the death penalty. If more than 50% of the public votes in favor of execution, Gaetal carries out the sentence, sparking a massive societal debate about justice, vigilantism, and the failures of the legal system. The series centers on the intense pursuit by Kim Moo-chan, a dedicated police team leader, and Joo Hyun, a sharp-witted cyber investigation officer, as they attempt to track down the masked vigilante. Alongside them is Kwon Seok-joo, a former legal scholar turned prisoner who has a complex, personal connection to the origins of the movement. As the death penalty votes continue, the characters are forced to confront the blurred lines between morality and murder, questioning whether the public has the right to play judge, jury, and executioner.