Starllight Glimmer has won, she has made Equestria into her world where no pony is different where everypony and everything is the same. Everypony never feel down, with Starlight controling Equestria only four still have their normal cutie marks.
Starlight won, or so she thought. Changing time without waiting for Twilight's return, she thought she succeeded. Upon leaving the past, she comes to a place she's never seen before. Fortunately, more than one pony in Equestria has fiddled with time.
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.