Yang Ling, a modern worker, accidentally enters the fantasy Dafeng Dynasty, and changes his appearance to become a night watchman who monitors officials and solves cases for the people of Dafeng - Xu Qian'an. With what he has learned in modern times, he uses scientific knowledge and reasoning skills to successfully solve bizarre cases and is known as the master of solving cases in Dafeng. In this world of Dafeng with demons, magic, treacherous hearts and undercurrents, he and his like-minded partners choose to face difficulties, dare to sacrifice themselves, and jointly fight against the dark forces of the court, speak for the people and justice, and work together to protect the stability of Dafeng.