Shen Ce, the Marquis of the Northern Frontier, commands an army of 300,000 troops and has guarded the border for years. This makes Emperor Xiao Heng deeply wary of him, so the emperor issues an imperial decree ordering Shen Ce's only younger sister, Shen Lingyi, to enter the palace as empress. However, Shen Lingyi is framed in the palace by Noble Consort Su Wanning, while the emperor regards her as nothing more than a pawn and cares nothing about whether she lives or dies. Shen Lingyi consequently suffers endless torment in the palace, but remains silent and endures it all to protect her elder brother. In the end, she freezes to death in the Cold Palace. Upon learning the tragic news, Shen Ce is overcome with grief. In a fit of fury, he personally leads 300,000 iron cavalry to the imperial capital, slaughtering his enemies. He forces the emperor to repent and admit his wrongdoing before his sister's grave, publicly clears her name and overturns the injustice, and permanently stations troops in the capital to protect his sister's honor even after her death.