In the tenth year of Shaoxing (1140), the balance between Song and Jin suddenly shifts. On the Caishi River, blood and fire mingle. Zhao Heng, an illegitimate son of Emperor Gaozong of Song who grew up among commoners, rises from a humble boatman to become the commander of the firearms corps. Amid the smoke of battle, he deciphers a surviving fragment of the Essentials of the Military Classics and rewrites the rules of war. Beneath the same moonlight, Liang Xueya, daughter of a maritime merchant in Mingzhou, conceals a vermilion bird mark burned into her right shoulder by a firearm. She is undercover as a Jin spy. She possesses a secret method for refining saltpeter and a gift for breaking codes, yet as she risks everything to save blueprints and protect ships, her fate becomes entwined with Zhao Heng's. When the three-barreled hand cannon roars seventy years ahead of its time and kite-borne scouts sweep across the blood-red sky; when a rebellion in the firearms corps at Dongting Lake erupts in smoke, and Li Qingzhao recites a revised version of “Summer Quatrain” on her deathbed; when the Manual of Heavenly Crafts and Deadly Weapons changes hands amid the flames of war, and sixty percent of the Tea and Horse Bureau's profits are used to build ironclad ships at Feishui... technology in gunpowder, eighty years ahead of its time, utterly overturns the century-long standoff between Song and Jin. She is a spy, he is a rebel. She burns her family's fleet to obtain Jin's defense plans; he takes the blame and disgraces himself to protect the firearms corps. Though the vermilion bird marks on their shoulders seem to answer each other from afar, they face a choice between life and death during the Yangtze River fire-ship battle in the eighth year of Shaoding (1148): pursue the Jin emperor, or save the one they love?
