Season 1

The Killing Vote for vicious criminals begins. The death penalty is carried out according to the vote, and the investigation by the Special Investigation Headquarters starts.

The second Killing Vote begins. The police struggle to stop the death penalty by Gaetal. The car containing the second victim and Mu-chan explodes.

Mu-chan injured in the explosion along with the second victim. Witnessing this, Joo Hyun falls into despair, and the story of Seok-joo in prison keeps repeating itself.

Mu-chan tries to find out the whole story of the current case by sending Joo Hyun, who was recruited in the special team, to Seok-joo. A video foretelling the third Killing Vote is emerging.

Seok-joo joins the police on the morning of the Killing Vote. The police are dispatched to rescue Captain Oh, who was designated as the victim, and they are one step closer to the identity of Gaetal.

Joo Hyun and Seok-joo chase after the person suspected. Mu-chan confronts Jin-wook, who tried to kill Captain Oh. The police announce that they have arrested Gaetal, but the true identity of Gaetal is revealed.

8 years ago, the case between Mu-chan and Seok-joo is revealed. The story of Seok-joo's young daughter dying and Seok-joo killing the culprit himself. And who the accomplice of the dead criminal is revealed.

Public support for the Killing Vote is growing stronger. The police realize Lee Min-soo was the one who sent letters to Seok-joo as Number One Fan. As soon as Mu-chan accuses Seok-joo of being the real Gaetal, Seok-joo escapes.

Min-soo steals the Killing Vote system as Gaetal's identity is gradually revealed. While on the trail of discovering who Gaetal is, Joo Hyun infiltrates Min-soo's secret room.

Lee Min-soo's investigation is sluggish due to Min Ji-young's interference. Gaetal tries to judge Min-soo by putting him in the Killing Vote.

Apart from the Killing Vote, Min-soo is killed by Min Ji-young's scheme. Seok-joo tries to commit suicide by placing himself in the Killing Vote, and Ji-hoon tries to stop it.

The majority votes to abstain from executing Seok-joo, and his Killing Vote is canceled. As Seok-joo is about to hand over the voting program, Chul-min tackles him, and they both fall deep under water. Meanwhile, someone holds a Gaetal mask in their hand, and they put it on. Who could it be?