Princess Yongle, Xiao Xuanning of Great Yan, has been cherished since childhood and longs for the companionship of a sister. Hoping to fulfill her wish, she arranges for Mu Jinyao to marry into the Eastern Palace. After the wedding, however, Mu Jinyao becomes jealous of Xiao Xuanning for being the sole recipient of the emperor's favor. She imprisons and humiliates the princess, conspires with the Southern Frontier delegation to ruin her reputation and force her into a political marriage, and stages her death along the way. To protect his position as heir, Crown Prince Xiao Jingheng turns a blind eye to his wife's crimes and blocks every avenue through which his younger sister might seek help. At the critical moment, a loyal maid escapes the palace to deliver the news, and the emperor leads the Imperial Guards to break down the gates and rescue his daughter. Xuanning uncovers the truth step by step through a broken hairpin, a medicine box, and forged documents. In the end, Mu Jinyao is executed, the crown prince is deposed and placed under house arrest, and the Sixth Prince succeeds him as heir apparent.