The three princesses were just doing their duties as princesses, when they're visited by a mysterious stallion. The stallion tells them that the entire world is going to be plunged into an endless sleep, and that there's another alicorn in Equestria. Before the princesses could ask him anything, the stallion vanishes.

Meanwhile, Shimmer has just moved to Ponyville, and is trying to get accustomed to everything. However, it's not easy to keep her secrets, what with all the nosy ponies and surprise parties. But everything turns to the unexpected when Celestia is looking for a fifth alicorn, and dark creatures start attacking Equestria, putting everypony into a sleep from which they don't awaken! Shimmer is the only one that the sleeping spells don't work on. Suddenly Shimmer is the only one who can stop the new evil. And if she fails to save everypony, the whole world will end up falling into an eternal slumber.