Chu Yi, the Chu family's younger daughter who has been separated for twenty years, has learned martial arts and medical skills in Cangwu Mountain since childhood. Following her master's orders, she disguises herself as foolish and goes down the mountain to recognize her family. Returning on a rainy night, she recognizes her sisters by means of a thigh-exclusive bite mark, but she has to face her parents affected by the Xuanming Palace's poison arts, as well as the fake young master Chu Jingxuan who usurps her identity and makes things difficult for her everywhere. While acting foolish and hiding her clumsiness, Chu Yi secretly investigates the truth behind the bone-corroding powder poison and the kidnapping of herself back then, protecting her three sisters who are suffering from a chronic strange poison. With villains in the dark pressing step by step, can she uncover the conspiracy and protect her own family?