In a battle with her older sister nearly 1000 years ago, Luna had to resort to banishing Celestia into the sun. In a vastly different Equestria, ponykind must prepare for the return of Celestia and the apocalypse she will most likely bring forth.
Second in the Pieces-verse. Following their victory over their terrible enemy, the new Mane Six must deal with the aftermath and its complications, including an even greater enemy.
Discord has won. Everyone in the human world is under his dominion, save for Sunset Shimmer whom he saved for last. Today the world, tomorrow Equestria.
Battling Starlight Glimmer, Twilight finds herself in another alternate timeline. Only this time, she finds herself in the Golden Oak Library with the Princess of Friendship: Sunset Shimmer.