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.