In the distant past, a group of European mercenaries are in the Far East in search of the mythical black powder that turns "air into fire", it the source of their future wealth in bringing it back to Europe. They are attacked by an unknown creature, with William, one of the mercenaries, able to kill the creature. Two of the mercenaries, William and Tovar, are captured by the local army, called the Nameless Order, who house them within the confines of the Great Wall. The Nameless Order informs them that the creature is called a Tao Tei, as a species who attack once every sixty years, this one specimen killed by William signifying their imminent attack. Tao Tei's survival is predicated on the soldier creatures gathering food to bring back to the Queen as nourishment. Although not stated to them explicitly, William and Tovar learn from Ballard, another westerner at the Wall, that they will be treated well but are not allowed ever to leave in the Nameless Order protecting the secrets of the Wall, Ballard who, like them, was a mercenary in search of black powder, he captured twenty-five years ago. As the Tao Tei initiate their attack, the Nameless Order executes their strategic defense, with most of their measures based on their position of the fortress that is the Great Wall. In viewing what is happening, William and Tovar begin to diverge in their thoughts: Tovar, with Ballard, sees the current turmoil as the perfect opportunity to escape stealing as much of the black powder that the Nameless Order has that they can carry, while William, seeing a new purpose in life in learning about trust from Commander Lin Mae, wants to stay and fight with the Nameless Order, it not a certainty that any of them being able to survive regardless of the path they take. This divergence places William and Tovar at odds with each other in carrying out their chosen paths.