The wicked Mare of Darkness, Nightmare Moon, has returned to the world and in a body all her own. Wielding the power of the enigmatic Alicorn Amulet, and with an army of shadowy creatures called The Animus at her disposal, she has turned Princess Luna into her thrall and warped the Crystal Empire into a nightmarish wasteland. From this new seat of power, she sets her sight on the very heart of Equestria.

While Princess Celestia rallies the ponies to fight back against the dark horde and does her best to maintain the Equestrian way of life, it falls to Twilight Sparkle and her friends to find a way to break the power of the Alicorn Amulet and free Princess Luna from Nightmare Moon's dominion. With only Luna's thousand-year old journal to guide them, they set out on a journey that will take them beyond Equestria as they seek to learn more about a dark, crystalline substance called midnium; a journey that will shed new light upon the literal darkest day in Equestrian history.

-part 2 in The Lords of Harmony series. takes place mid-season 3, before Keep Calm and Flutter On.
-this story assumes there is a one-year time frame for each season of the tv show, give or take a couple months
-edited by BronyDad. Many thanks to him! Give his stuff a look, as well!