Xiao Chengzhao, the legitimate eldest daughter of Prince Yu's household, loses her mother at a young age and suffers under the harsh treatment of her stepmother. She is forced to disguise herself as a man and enter the capital in place of the heir apparent, serving as a hostage and study companion in the Eastern Palace. Protected by Crown Prince Xiao Zhi, she uses her medical expertise and financial skills to help him curb the power of the regional princes. After being seriously injured while protecting the emperor during the spring hunt, her identity nearly comes to light, but an imperial physician helps conceal the truth. Investigating the old case surrounding her mother's death, she discovers that Prince Zhao and her uncle Xiao Wu have conspired to rebel. Even after her identity is exposed, the crown prince chooses to join forces with her and devise a plan. At the Empress Dowager's birthday banquet, she exposes the evidence of the conspirators' crimes. After Xiao Zhi ascends the throne, he clears her mother's name and punishes the traitors. Having avenged her mother, Xiao Chengzhao makes a three-year pact, leaves the capital to travel the realm, and awaits their reunion in a prosperous age.