Civil engineer Shen Yan travels through time to the turbulent Da Qian era, becoming the magistrate of the dilapidated Heishi County. Facing the desperate situation where border troops demand grain and the lives of the common people hang by a thread, he relies on his professional knowledge to find groundwater, uses konjac to resolve the crisis, and cleverly uses hygiene knowledge to save camp soldiers, relieving the heavy burden of grain collection. Standing on the wasteland, he makes salt to trade for grain, builds waterwheels, reclaims farmland, fights against the treacherous Zhou family, subdues mountain bandits to develop coal and iron resources, and wholeheartedly builds Heishi City. However, with internal sabotage by hostile merchants and external pressure from 30,000 northern barbarian cavalry about to press upon the border, the new city without solid walls is about to face a test of life and death.