Spike finds a spell that can age him one hundred and fifty years, but when he tries it, he finds himself in a future where the ponies are at war with the dragons.
What do you do when you discover that a mistake you'd thought long fixed is still at large? If you're Twilight Sparkle, you bend time and space to fix it. With friendship, of course.
At the height of the Great Crystal War, Lieutenant Rarity finds in her camp a strange mare claiming knowledge of how to end it. But first, they must survive the coming battle.
Between Ponyville and Appaloosa, there is a bridge that if one were to walk across on a moonless night, they would never return. A reporter goes to investigate. This is what he finds.
Each time Twilight tries to stop Starlight, she fails and is flung to a new, twisted Equestria, each one worse than the one before, until she lands in one that isn't worse. The only real difference is that her castle isn't there. But the library is.