The story is set in the Song dynasty and at the beginning of the Jurchen-ruled Jin dynasty's invasion of northern China. The first part revolves around the friendship of two men, Yang Tiexin and Guo Xiaotian, who became heroes in their own right as they fought the Jin invaders. The bond between the duo is so strong that they pledge to each other that their unborn children will become either be sworn siblings (if both are of the same sex) or a married couple (if they are of opposite sexes).

The story focuses on the trials and tribulations of their sons after Guo Xiaotian's death and Yang Tiexin's disappearance.