During the era of the Renzong Emperor, a band of European mercenaries embarks on a perilous journey to China in search of gunpowder. Their quest takes a dire turn when they are suddenly attacked by a monstrous creature just north of the Great Wall. Only Irishman William Garin and Spaniard Pero Tovar manage to survive this horrific encounter, severing the beast's arm to bring back as a trophy. Upon reaching the Great Wall, the two are captured by the Nameless Order, led by General Shao and Strategist Wang. This ancient order is dedicated to fighting against the Tao Tie, alien monsters that descend upon the land every sixty years, having arrived from a meteorite. Surprisingly, the monsters have launched their attack a week early this time, catching everyone off guard.
As a wave of Tao Tie storms the Wall, chaos ensues. During this fierce battle, Garin and Tovar are freed from captivity by Ballard, an Englishman who had come east twenty-five years prior and has since been held captive. Demonstrating exceptional combat skills, Garin and Tovar aid in defending the Wall, even saving the life of a young warrior, Peng Yong, while slaying two monsters in the process, which earns them the respect of the Nameless Order. The conflict incurs heavy casualties on both sides until the queen of the monsters withdraws her forces.
Under the cover of night, two Tao Tie manage to scale the Wall, resulting in the death of General Shao and placing Commander Lin at the helm of the Nameless Order. In this time of crisis, an envoy from the capital arrives bearing an ancient scroll, suggesting that the monsters can be pacified using magnets. Wang postulates that the stone Garin possesses allowed him to defeat the Tao Tie he encountered. In a bold plan, Garin proposes to capture one of the creatures alive to validate the theory, causing a delay in their intended escape, much to Tovar's frustration. Nevertheless, Tovar joins Garin in the endeavor despite Ballard's reservations.
As the next skirmish with the Tao Tie begins, the Europeans succeed in capturing a monster, thereby confirming Wang's theory. However, their victory is short-lived as the Imperial envoy claims the creature, taking it back to the capital to present before the Emperor.
Unbeknownst to them, the previous monster attacks were merely a ruse; the Tao Tie had been tunneling underneath the Wall. While Commander Lin investigates, Tovar and Ballard seize the opportunity to steal black powder and escape, knocking Garin unconscious in the process. Accused of betrayal, Garin is imprisoned within the Wall. Meanwhile, Ballard backstabs Tovar and is later captured by bandits who accidentally ignite the stolen black powder, leading to a deadly explosion.
In the capital, the captured Tao Tie awakens, signaling its queen, who orchestrates an all-out assault. The Nameless Order races to the capital, where Lin takes charge of the response, deploying hot-air balloons and freeing Garin just before heading off to confront the threats. Wang advises Garin to alert the world outside, but Garin instead boards the last balloon along with Peng and Wang, racing to save Lin from the grasp of the monstrous horde.
In a daring plan to eliminate the queen, Wang proposes to use the captured Tao Tie as a weapon by tying explosives to it while luring it with meat to draw the queen out. As they make their way, they are ambushed by the Tao Tie, resulting in a brave sacrifice from Peng to protect his comrades.
In a tense moment, Lin and Garin ascend a tower, where Garin intends to detonate the explosives with a well-placed arrow. Wang selflessly sacrifices himself, allowing Lin and Garin to reach the heights needed. Despite encountering resistance from the queen's guards, Garin ingeniously throws the magnet, creating an opening in their defenses, which allows Lin's spear to penetrate. With the queen defeated and the remaining Tao Tie dispatched, Garin is granted the opportunity to return home. In an unexpected twist, he opts to bring Tovar along instead of claiming a reward of black powder, much to Tovar's dismay.
