Shen Lan, a top modern-day special agent, travels through time to the Great Yan dynasty and becomes the young marshal of the Shen family, whose entire household has been condemned to execution. Escaping death at the execution ground, she forms an alliance with the seventh prince, Xiao Heng, who has been lying low and pretending to be insane. Together, they storm the Jingzhao Prefecture, investigate the Eastern Palace, expose a valley of private troops, and dismantle a poisoning plot. They take on the Crown Prince and the powerful chancellor Liu Yuan head-on, gradually uncovering the truth behind the wrongful case against the Shen family, stirring up the imperial court, and ultimately receiving an imperial decree to confront the crisis on the northern frontier together.