Plot
During the reign of Emperor Renzong, a group of European mercenaries travels to China, searching for gunpowder. A few miles north of the Great Wall, they are attacked by a monster. Only Irishman William Garin and Spaniard Pero Tovar survive. They sever its arm and bring it with them.
Upon reaching the Wall, they are taken prisoner by the Nameless Order, led by General Shao and Strategist Wang. The Nameless Order exists to combat Tao Tei, alien monsters that arrived from a meteorite and attack once every sixty years. The Order's commanders are surprised by the monsters' first assault, which has come one week early.
Shortly after, a horde of Tao Tei assail the Wall. During the battle, Garin and Tovar are freed by Ballard, an Englishman who came east twenty-five years earlier and has stayed ever since. Garin and Tovar display amazing battle skills, saving the life of young warrior Peng Yong and slaying two monsters, which earns them the Order's respect. Both sides sustain heavy losses before the monsters' queen aborts the attack. The three Europeans secretly plan to steal gunpowder and flee during the next monster attack.
That night, two Tao Tei reach the top of the Wall. General Shao is killed so he places Commander Lin in charge of the Nameless Order. An envoy from the capital arrives with an ancient scroll that suggests that the monsters are pacified by magnets. Wang believes the magnetic stone Garin carries enabled him to slay the Tao Tei he encountered. To test the hypothesis, he suggests they capture a Tao Tei alive and agrees to help. This delays the escape plans, angering Tovar, who nevertheless agrees to assist Garin.
In a new fight with the Tao Tei, the Westerners capture a monster and prove the theory. However, the Imperial envoy claims the creature and takes it to the capital to present to the Emperor.
It is revealed that the previous attacks had been a distraction so that the Tao Tei could dig a tunnel at the base of the Wall. While Lin investigates, Tovar and Ballard steal black powder and escape, knocking Garin unconscious for trying to stop them. Garin is arrested and jailed for his apparent betrayal.
Some distance away, Tovar is abandoned by Ballard who is captured by bandits who later accidentally ignite the powder causing an explosion. At the capital, the envoy presents the captive Tao Tei to the Emperor. The creature awakens and reveals its position to its queen, who signals the Tao Tei to attack.
Lin orders the use of hot-air balloons to rush to warn the capital and sets Garin free before embarking. Wang tells him to warn the outside world, but he boards the last balloon with Peng and Wang. They arrive just in time to save Lin from being devoured. Wang proposes a plan to kill the queen by tying explosives to the captured Tao Tei and giving it meat to be delivered to the queen. En route, a horde of Tao Tei attack the band, and Peng sacrifices himself to save the others.
After releasing the captive Tao Tei, Lin and Garin climb a tower so that he can detonate the explosives with an explosive arrow. Two of Garin's arrows are deflected by the Tao Tei queen's bodyguards, and Wang sacrifices himself to buy time for Lin and Garin to reach the upper floors. In a last gasp, Garin throws the magnet into the horde, creating a gap in the shields for Lin's spear carrying their last explosive to get through. The queen is killed, and the rest of the horde dies.
Garin is allowed to return home and elects to take the apprehended Tovar with him instead of a reward of black powder, much to Tovar's annoyance.
