For over a thousand years following her ascendance to power, Twilight had lived in the shadow of the Celestial Sisters, happy and content to drag Equestria kicking and screaming into a bright, technologically advanced future beyond the High Frontier. When Celestia suffers an accident at the hands of one of Twilight's inventions, presumed lost in the interstellar gulf, Luna abdicates, intentions unknown.

Now Twilight must rule alone, facing new threats whilst attempting to maintain order and harmony not only on Equestria, but the many settled worlds under her aegis.