Shen Qingyan, a modern postgraduate student in history, transmigrates into the cannon-fodder wife of the Marquis of Yongning. The original wife was infatuated with the marquis and had her estate seized and her children harmed by the secondary wife, Su Lianyue. Relying on the law and evidence, Shen Qingyan fiercely defends her fief, intercepts poisoned pastries, catches spies within the household, and exposes Su Lianyue as an enemy-state infiltrator. She also faces a collateral branch's attempt to seize the marquis title, border warfare, and political frame-ups at court. Amid the struggle for the throne, she maintains neutrality and helps put down the Seventh Prince's palace coup. Xiao Heng ultimately voluntarily relinquishes his military authority, and together the couple protects their children, their homeland, and their country.