A thousand years ago, Princess Celestia banished her sister to the moon, that much we know. What wasn't known, and what Celestia kept secret was that before her banishment, Luna had given birth to a foal. Now a thousand years later, as Nightmare returns to Equestria to bring about Eternal Night. Twilight Sparkle, protege of Princess Celestia, struggles against the tyranny of this ancient foe. But how will she be able to save herself and her friends when the truth of this ancient legend crashes down upon her? Twilight will have to confront herself...and her heritage.