Caught in the throes of an epic pony prank war, Twilight decides to use a new spell of hers to get even with a certain white mare. But one stop off to prank Rarity turns into a call for help, and a budding romance for the two unicorns, with a few feline perks. But Twilight should really have stopped with that spell long ago, because now she and Rarity face an enemy they never saw coming.