Lu Chen, a death-row prisoner, is exiled to the frigid frontier at Hanguan. There, he is repeatedly set up and sent to his death by Deputy General Han Lie and Military Supervisor Zhao Yanli. Relying on his extraordinary strategic mind and engineering skills, he leads a group of low-ranking death-row prisoners in defending the battered Blackstone Fortress, ambushing and crushing the Northern Di cavalry scouts, and exposing corruption and traitors within the army. When court officials withhold provisions and transfer away the garrison troops, Lu Chen tears up the imperial edict and resolutely holds the defensive line. He captures a Northern Di prince alive and devises a deadly ambush in White Wolf Valley, dealing the enemy a devastating blow. With Yun Zhao's help and an ancient joint-defense map inherited from her forebears, they rally civilians and battered soldiers to build their defenses. After the main Northern Di forces are defeated, Lu Chen accepts a commander's seal forged collectively by the people, becoming the uncrowned guardian of the northern frontier. Yet a crisis in the imperial court is looming.