As Twilight wanders within the ruins of the Castle of the Two Sisters, she is blissfully unaware that she is about to discover a secret that has stayed buried for close to a millenium...and will change her understanding of Celestia and Luna - forever.
Eight months after the events of Equestria Girls 2: Rainbow Rocks, a new threat arises that not only threatens Equestria, but also every other dimension in existence - and it's Twilight Sparkle!
As Twilight wanders within the ruins of the Castle of the Two Sisters, she is blissfully unaware that she is about to discover a secret that has stayed buried for close to a millenium...and will change her understanding of Celestia and Luna - forever