Set in imperial China, amid the long wars between the Jurchen-led Jin Empire and the Han-majority Song Empire, the tale follows two sworn brothers who vow a lifelong bond for their unborn children: if the children are of the same sex, they will be sworn siblings; if they are of opposite sexes, they will become a married pair.
One day, Yang Tiexin's wife, Bao Xiruo, saves a wounded Jurchen warrior who turns out to be Wanyan Honglie, the Jin prince. Honglie's later vengeance drives his troops to strike the brothers’ village, leaving Guo Xiaotian dead and Yang Tiexin missing in the chaos that follows.
Guo Xiaotian's pregnant wife Li Ping wanders into Mongolia, where she gives birth to Guo Jing, who grows up under the care of Genghis Khan. He trains in martial arts with the legendary Seven Freaks of Jiangnan and Ma Yu of the Quanzhen School, while also learning archery from Jebe. The Chinese title of the novel is derived from an incident in Guo Jing's youth when he shot two eagles with a single arrow.
Bao Xiruo is captured by Wanyan Honglie, who marries her, and she gives birth to Yang Kang, who is raised as a Jurchen nobleman. Although he is mentored by Qiu Chuji of the Quanzhen School, he secretly learns the dangerous "Nine Yin White Bone Claw" technique from Mei Chaofeng.
Guo Jing is honest, loyal and righteous, but outwardly slow-witted. In contrast, Yang Kang is clever but treacherous, and he soon finds himself plotting with the Jurchens to conquer his ancestral homeland. They eventually meet their respective lovers, Huang Rong and Mu Nianci, and the central journey follows Guo Jing and Huang Rong as they navigate the martial-arts world, crossing paths with the era’s most powerful figures, the so-called "Five Greats." Along the way, Guo Jing and Huang Rong pick up techniques from renowned masters, and Guo Jing learns more about the mystery surrounding his father’s death.
Yang Kang’s ambitions push him toward an alliance with the Jin invaders, driven by a hunger for wealth, fame and power, while he resists acknowledging his Han heritage. His treachery gradually clashes with Guo Jing and Huang Rong, revealing itself across the story.
With Guo Jing's steadfast resolve, the Mongols eventually topple the Jin Empire and turn their attention toward the Song. Guo Jing refuses to aid the Mongols in attacking his homeland and instead returns to the Song to help defend against the looming invasion. Yang Kang dies from poisoning after attempting to strike Huang Rong; his palm strikes inadvertently foul his own fate when his attack damages Huang Rong’s spike-protected armor. He leaves behind Mu Nianci and their unborn son, whom Guo Jing names Yang Guo. The Mongol invasion is briefly halted when Genghis Khan dies.
