Shining Armor gets a letter from Princess Celestia, asking him to Canterlot. There, he learns that Discord -- a creature that is the living embodiment of chaos -- has returned after a thousand years. Now he and his friends must use The Elements of Harmony to stop Discord from turning Equestria upside down (possibly in a very literal sense).
There's only one major problem: The Elements are missing.
Start of Season 2 of "Friendship is Shining."