After discovering that the fabled Kingdom of Harmonia really did exist, Princess Celestia grants Twilight the title Princess of Harmonia, and tasks her with leading an expedition into the Everfree Forest to discover what caused the kingdom that created the Elements of Harmony to collapse.

After becoming an alicorn, Twilight heads to the Canterlot Library for information about what she has become. What she finds is a confusing pile of myths and contradictions. To get her answers she will have to hear the truth from Luna and Celestia themselves.