Andy Lau stars as Zhao Zilong, a veteran general of the Kingdom of Shu who took a last stand against the invading forces from the Kingdom of Wei. Maggie Q is the fictional Cao Ying, a granddaughter of the warlord Cao Cao, whose son Cao Pi became the first emperor of the Kingdom of Wei.
The story depicts an alternate history, following the events that unfolded in the Three Kingdoms era through the life of the legendary Shu general Zhao Zilong. He began his military career as a soldier in warlord Liu Bei's army. Zhao Zilong once displayed his fine spear skills to Liu Bei in a small face-off with officers Guan Yu and Zhang Fei. This impressed Liu Bei, and he decided to promote Zhao Zilong to the rank of a general. Zhao Zilong was bestowed with the 'All Piercing Spear'.
Zhao Zilong scored his first victory in battle by outwitting Cao Cao at the Battle of Changban. He managed to rescue Liu Bei's son, A Dou from the clutches of the forces of Cao Cao by fighting them single-handedly. Cao Cao's life was put in great peril and he also lost his personal weapon to Zhao Zilong. Cao Ying, who had witnessed Zhao Zilong's acts, swore to help her grandfather regain his lost pride by capturing him alive.
As time passed, Zhao Zilong never lost any battle he fought in, thus earning himself the title of 'The Undefeated General' (常勝將軍). Cao Pi forced the last ruling Han emperor to abdicate in his favour and proclaimed himself Emperor of the Kingdom of Wei. Thereafter, Liu Bei assumed the title of Emperor of Shu-Han as a spiritual successor to the fallen Han dynasty by carrying on the family name. Zhao Zilong joined the ranks of Guan Yu, Zhang Fei, Ma Chao and Huang Zhong to be one of the Five Tiger Generals sworn to defend the Han imperial family.
Years after Zhuge Liang's first failed Northern Expedition, he embarked on a second expedition. Zhao Zilong had reached the age of 71 by then, hence Zhuge Liang had doubts about allowing him to join in the expedition. However his persistence ensured him a role in the expedition. The Chancellor handed him two satchels, instructing him to open them as per situations. Zhao Zilong set forth on the expedition expecting to achieve a major victory once more. His first feat was the slaying of the four sons of Wei general Han De (similar to the novel). As Han De retreated, it became obvious that it was a ploy to lure Zhao Zilong into a trap, planned by the Wei commander Cao Ying. Zhao Zilong was forced to retreat to the Yellowbird Peak. It was there that Zhao Zilong pitted his last strength against Cao Ying.
In a single one-to-one duel, Zhao Zilong fought Cao Ying but decided to let her go. During the fight, the undefeated general received a battle scar for the first time ever in his career. The surbordinate generals of Zhao Zilong engaged in a fierce battle with the Wei forces, but were defeated after Cao Ying sacrificed Han De to bring gunpowder into the battlefield. All was lost for Zhao Zilong. He stripped off his armour, picked up his Piercing Spear, and charged towards the Wei forces in a last ditch effort, swearing to defend the Yellowbird Peak, and the dignity of the Kingdom of Shu-Han to the last general and last man.