A lawyer with a ten-percent winning rate is caught up in a murder case and becomes the notorious and genius con artist, Big Mouse, overnight. In order to survive and protect his family, he tries to reveal the true colors of the privileged people involved in a huge conspiracy.
After the culprit in the Joker Murder Case, Jeong Man-chun is killed post-trial, jurors start dying. Detective Ryu Sung-jun, suspected of the crime, seeks the true killer with his brother and a juror.