The drama is based on the principle of "non bis in idem" (a general legal principle that a case once handled should not be tried again). It tells the story of Han Jong-gu, the suspect in a murder case of a woman assigned to Choi Do-hyun (Lee Jun-ho) five years ago, who was charged with murder but was eventually found not guilty. Han Jong-gu was then charged again for another murder case. During the trial, he confessed that he was the real murderer of the murder case five years ago, but he could not be punished because of the "non bis in idem". It tells the ironic story of the law that cannot punish the criminal even if he confesses.