Muskets guard the lonely city, iron blood protects the common people. The modern arsenal system awakens, Jiang Ming time-travels to become the heir of the Northern Border Prince's Mansion, only to face an imperial commissioner raiding his house at the start, with his sister in danger of being reduced to music registry. He subdues the imperial guards with Desert Eagles and high-explosive grenades, gathers veteran soldiers, seizes the four gates by night, and cleverly breaks the encirclement. Facing powerful officials and strong enemies from the grasslands, he moves step by step, builds a firearm workshop, promotes new policies, trains a new army, and wins against the odds with fewer troops. In the end, he leads his army north, clears his father's name, guards the city to protect the people, and creates a new era.