Episode List: http://mlp.draconequus.com
Princess Celestia learns of the reappearance of the Crystal Empire, which had disappeared over a thousand years ago as the last act of the evil King Sombra (Jim Miller) prior to his banishment; Celestia fears Sombra will return and use the power of the Empire to take over Equestia. She summons Twilight Sparkle and directs her to join her friends, Princess Cadance, and Shining Armor at the Empire to help protect it, as a test of her abilities. At the Empire, Cadance attempts to maintain a spell to prevent the shadowy form of King Sombra from entering. Twilight and her friends talk with the brainwashed residents of the Empire, and learn of a Crystal Fair which used to enlighten the hearts of the Empire and protect it from the King. Only too late does Twilight realize that the missing Crystal Heart was the centerpiece of the fair and a necessary artifact to protect the city.
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The Crystal Empire part is about how one of the main seven saves the Crystal Empire.