As Equestria recovers from what has been termed the Second Eastern Rebellion, Princess Twilight Sparkle shares the letters written between herself and her rebellious former student.  The Zephyrites, followers of the prophet Warm Zephyr, nearly succeeded in purifying their land of all non-ponies.  Within these letters lies the reason five hundred ponies fled the land of Equestria.  And a question is debated which will define the future of Equestria: what is the true meaning of Friendship?