It tells the story of the free and undisciplined ranger Yun Zhan and his master who are implicated in a bizarre case. They are accidentally suspected by the princess Shi Qiutong and the guard An Xuewu as the murderer. In the process of proving his innocence, Yun Zhan gradually finds the direction of his life and meets Shi Qiutong. They joined forces to solve the strange case, and since then they have shouldered their own missions and responsibilities to protect the safety of the people in the imperial city.