Ultra-light American diesel gunwings can hold their own against Australian human-powered battle computers and a tram-based net. But they are helpless against the ultimate doomsday machine: The Miocene Arrow.

In a fortieth-century America of ancient kingdoms with opulent courts, hereditary engineering guilds, and rigid class distinction in warfare, a centuries-old balance of power is shattered by a few dozen Australian infiltrators. Against a rich backdrop of war, chivalry, conspiracy, and a diesel-powered arms race, a dangerous secret alliance has formed. Now the unlikely trio of an airlord, an abbess, and a fugitive are joined together in a desperate race against time to stop the Miocene Arrow from being launched -- and save the world in the process.