A stranger from another world arrives in Equestria hoping to awaken a long forgotten power while Princess Mi Amore Cadenza and Prince Shining Armor deal with some troubling changeling activities. Meanwhile Queen Chrysalis is trapped in a castle with a maze of doors unable to escape, however she may soon find herself free ready to take revenge on the two ponies that ejected her from Canterlot Castle. Yet the stranger may have other plans, forcing the crystal ponies and changelings to toss aside their conflicts and join forces to stop a greater evil.