Overnight, a palace coup occurs, and the former princess Changle loses all her family members, deposed and exiled to the northern frontier. Her former lover, Pei Yan, participated in the seizure of power and became the crown prince of the new dynasty. Changle is forced to separate from her only remaining maid and steps alone into the desolate northern frontier. Facing famine, popular grievances, and barbarian invasions, she transforms from a ruined princess into a city-defending female general. Five years later, Pei Yan returns to the frontier to save the city. As old lovers reunite, political schemes, blood feuds, and the truth about the palace coup of that year gradually emerge. One defends the city and protects the people, while the other carries the rivers and mountains of the new dynasty. Can they still return to the past?