When the border city suffers a snow disaster and lacks food, the concubine's sister Xu Yunqi forges documents, seizing the commercial grain shops left by Xu Zhiwei's mother as her own disaster-relief dowry, and also steals her engagement. Xu Zhiwei faces misunderstanding by the entire city, yet discovers the grain is poisoned by the Northern Desert Commercial Alliance, intending to collapse the border army. Relying on account books and commercial connections, she unites with military families and scout Xie Linchuan, layer by layer uncovers the conspiracy, defeats external enemies, settles accounts with a crowd of villains, reshapes the border city's grain route, and guards the people of the entire city.