In Taipei, a factory worker is murdered on her way home. Detective Koh Kang-young believes she died from a venomous snake bite based on marks on her neck, but reporter Lee Ok-jung challenges this in her article. This leads to frequent meetings and a friendship between Koh and Ok-jung. Then, two more women are killed the same way, with Ok-jung unable to explain her whereabouts during each murder. As a third murder occurs, Detective Koh uncovers a shocking truth about Ok-jung's past: as a child, she was bitten by a unique snake, granting her the ability to kill by mimicking its bite.