Based off Miao Juan's novel. In Tang Dynasty, the chivalrous eldest daughter of the Assistant Minister of Revenue, Ye Yuan An, saves Mu Le, an amnesiac young man of mysterious identity. Yuan An takes Mu Le in as a family servant, and the latter swears his loyalty to her. Along with Zhao Lan Zhi, a constable, the trio solve cases after cases together. But what is Mu Le's true identity?