When the Jin dynasty, governed by the Jurchen, first invaded northern China, the story takes place during the Song dynasty. The friendship between Yang Tiexin and Guo Xiaotian, two men who turned out to be heroes in their own right while battling the Jin invaders, is the focus of the first section. The couple's relationship is so strong that they make a promise to one another that their unborn children will either become married couples or sworn siblings if they are of the same sex or opposite sexes. After Guo Xiaotian's passing and Yang Tiexin's abduction, the plot mostly follows their sons' struggles.
