Yun Tang, the legitimate daughter of the Yun family, took the initiative to marry into Prince Su's palace on behalf of her concubine who had run away from marriage, with the goal of finding out the cause of her late mother's death; on their wedding night, the prince Pei Heng tried with a sword, but Yun Tang pretended to be weak and passed; she discovered that the prince was poisoned by a strange poison, and every time the moon was full, the poison made him look like a madman; Yun Tang used medical skills as a breakthrough , gained the trust of the crown prince; Liu Ruolan, the side concubine of the palace, had been harmed many times, and Yun Tang designed her to be banned; the prince and the third prince competed for the throne, and Prince Su's palace was tainted and concealed weapons; Yun Tang used a secret passage to help the crown prince transfer evidence; she accidentally found an old letter in the secret compartment of the prince's study, and mentioned And the old grudge between the Queen Mother and King Su; Yun Tang followed the clues and found out that his mother was once a maid of the Queen Mother, and was silenced for witnessing the Queen Mother's affair with a foreign minister; the Crown Prince confessed that the Queen Mother was responsible for his poisoning, in order to control King Su; the two formed an alliance, and they fell in love with each other; the Crown Prince was a merit-grabbing assassin. During the assassination attempt on the crown prince, Yun Tang defended him from an arrow and was injured. The crown prince fought back angrily and joined forces with the three princes to expose the prince's collusion with foreign enemies. The queen mother intervened in politics behind the curtain, and the conspiracy was exposed. In the end, the queen mother was imprisoned, the prince detoxified, and Yun Tang killed his enemy. The two resigned their titles and lived in seclusion in Jiangnan for the rest of their lives.
