When Equestria is threatened with an invasion of all its greatest enemies, Celestia and Luna are forced to turn to the only ally with a chance of helping them: Humans. The only question left now is whether any of Equestria will be left to save.
After the events of Project: Sunflower, Erin returns to Ponyville to study magic. Meanwhile, something is stirring on the newly-discovered world of Harmony.