The Book of Wumu is a fictional military treatise written by the Song general Yue Fei. The book is highly sought after by the Jurchens of the Jin dynasty. Guo Jing uses the knowledge he acquired from the book to defend the Song dynasty. Before his death, he hid the book in the blade of the Dragon Slaying Saber. Nearly a century after the Battle of Xiangyang, the book comes into Zhang Wuji's possession. Zhang uses one of the strategies in the book to defeat Yuan forces at the siege of Mount Song. He passes the book to Xu Da, who studies it and becomes a brilliant military leader. Xu Da leads rebel forces to overthrow the Yuan dynasty and becomes one of the founding pioneers of the Ming dynasty.