Humanity is nearly extinct, with nearly three fourths of the world taken by the ponies, their barrier and conversion potion, many have either given up or looked to cybernetics which prevent conversion but doesn't allow for them to go through the barrier. But there is a small group of humans, and ponies who have given up on their own kind, who instead look to the stars for a solution.

When the Gates of Tartarus open and the demon armies assault Equestria and her ponies, Princess Celestia will respond quickly and efficiently. This causes Twilight to wonder if Celestia already knew that the demons were going to come. Why would Celestia keep this hidden from everypony and why would she keep it hidden from 'her faithful student'. As Celestia initiates a martial law and a draft that seems to only pick specific ponies, Twilight's 'wonder' quickly turns to horror as she herself is drafted and sent to training. She soon learns that that Tartarus is so much more then just a prison for evil beings and that it's purpose is far more nefarious then she previously conceived.