Canterlot is in ruins. Thousands are dead, with millions more to follow. When the Pony of Shadows appeared in the real world it destroyed Canterlot and set its sights on the rest of the world. This wasn't the end, however; Princess Celestia and Princess Luna enacted one last measure to stop this calamity from occurring. They used their combined ability to turn back the clock and give the one at the center of it all a chance to change the future.