When Twilight Sparkle gets her element of harmony stolen by Sunset Shimmer, a former student of Princess Celestia, she travels through a mirror and finds herself in a different reality. Here, magic is completely different, cutie marks don't exist, a strange cult rules everyday life, and Celestia rules alone. Soon Twilight finds out there is something deeply wrong with this world, rooted in a mysterious prophecy from when the alicorns disappeared...