The great fire at the Fengyi Palace exposes an old case of swapped infants. Zhao Chong points out in the imperial court that the crown prince Xiao Jingheng is not of royal blood, and the true imperial prince Xiao Jingyao returns to his clan to ascend the throne, while Xiao Jingheng is stripped of his title and exiled to Anxi. Along the way, after being ambushed, he investigates the Pingchang disaster relief grain and the official granary deficits, exposes the ceding of territory to subsidize taxes and the secret pact with the Shuojun army, and leads the soldiers and civilians to defend the city against enemies. His fiancee Shen Qingtang stays in Beijing to investigate the old archives of the Fengyi Palace, cooperating with him from the inside and outside. Ultimately, Xiao Jingheng raises an army to enter Beijing to depose the emperor, Xiao Jingyao abdicates, the new administration stops harsh taxes and abolishes ceded territories, and Xiao Jingheng ascends the throne to govern and revitalize the imperial court.