Su Fu, a modern engineering graduate student, travels back in time and becomes a foolish concubine-born daughter. To escape an arranged marriage, she pretends to be insane, but the emperor personally selects her to marry Xiao Che, the notorious General Who Guards the North. Using her modern knowledge and her special ability to deduce the optimal solution simply by touching physical objects, she improves fire walls, develops military weapons, and exposes spies on the frontier. From a laughingstock of the army, she grows into the ingenious Lady. Facing an invading army of one hundred thousand Northern Di warriors and the threat of massive cannons from the Western Regions, she fights alongside Xiao Che, repeatedly defeating powerful enemies with repeating crossbows, thunder bombs, and improved heavy cannons. In the bitter cold of the frontier, she finally establishes herself and wins both respect and love.