One night in Taipei, a female factory worker is killed on her way home. Koh Kang-young, the lead detective, concludes that she was killed by a poisonous snake from the bite marks left on the victim's neck. Reporter Lee Ok-jung rebuts his theory in her article. Through this incident, Detective Koh and Ok-jung meet frequently and they become friends. Afterwards, two more women are killed in the same manner. It is revealed that Ok-jung can't account for her whereabouts for each murder. When another murder is committed, Detective Koh finds out the truth about Ok-jung. When Ok-jung was three, a unique snake bit her. Therefore, she kills people by biting them like a poisonous snake.