Shen Zhiwei, a female doctor of applied chemistry, transmigrates one day and becomes a concubine-born daughter in the Shen household, where her birth mother died young and her legal mother holds all the power. Faced with her legal mother Madam Wang’s arrangement for her to marry in place of another woman as a good-luck bride to the reportedly sickly, dying prince Gu Zhao, she immediately packs up her valuables and flees north toward Shuoyun City, relying on a modern person’s courage and her knowledge of chemistry.
She does not know that the “sickly prince” Gu Zhao is the young boy she rescued in the back alley of the Shen residence when he was six. He has spent years lying low in the palace, pretending to be ill to protect himself while plotting in secret. He had originally planned to use the auspicious marriage to shelter her beneath his wings, but he never expected her to dare flee from the wedding. Gu Zhao is not angry. Instead, he smiles and picks up his brush to write a letter to Xiao Zhi, the General Who Defends the North.
In Shuoyun City, provisions are being embezzled and military morale is in turmoil. Xiao Zhi was born to a poor family and rose to become a general through military achievements, yet the imperial court views him with suspicion. After Shen Zhiwei arrives, she uses her chemical knowledge to improve gunpowder, refine salt, and make fertilizer from nitrate-rich soil, helping Xiao Zhi stabilize the frontier step by step. Xiao Zhi goes from wariness to admiration, and from admiration to falling in love. The two stand shoulder to shoulder amid snowstorms and the flames of war.
Meanwhile, in the capital, Gu Zhao continues pretending to be ill while secretly sending provisions and relaying information to the northern frontier, protecting in his own way the girl who once saved his life and now saves his heart. The fates of three people quietly intertwine amid political schemes and a chaotic era.
