Twilight Sparkle wakes up one day to realize she's being visited by Celestia's Royal Guards. The Keepers of Harmony are needed in Canterlot to investigate what happened in the castle's Inner Sanctum, where the statue of Discord was being held under heavy guard. The only possibility is that someone came in the sanctum from outside, and freed him. The Princess sends them to find Discord, and defeat him for good, realizing that he is too dangerous to be contained. They set out to find him, and on the way they realize that there is much more going on than they thought. Discord's escape is only the tip of the iceberg.