A premeditated murder case turned the third-rate lawyer "Big Mouth" Park Changhao (Lee Jong Suk) into a genius fraudster "Big Rat" overnight. He was framed and sent to prison, where he turned evil and became a prison boss, fighting evil with evil and fighting the dark forces. In order to save her husband, his wife Gao Weihu (Lin Yuna) teamed up with him to investigate the case, and the couple vowed to uncover the mastermind behind the scenes.