Shen Ruojin is the legitimate daughter of the Marquis of Linyang. Having lost her mother at a young age, she was raised by her maternal grandfather, General Shen, in the western frontier. On her wedding day, her intended husband, Pei Jing, elopes with her half-sister, Mu Yunwei, while Qin Lang, the young prince of the Prince of Zhenbei's household, who has come to marry Mu Yunwei, is left waiting outside. Shen Ruojin makes a swift decision and exchanges brides with Qin Lang on the spot. Not long after their wedding, she receives a secret letter revealing that her grandfather's troops are trapped at Luoyue Pass. She sets off alone on a thousand-mile journey to the western frontier, with Qin Lang following close behind. Together, they seize the military tally, open the city gates, rescue the Shen family army, and launch a counterattack against Xichang. Along the way, they discover a clue hidden inside a lotus lantern suggesting that her third elder brother may still be alive.