While in the Crystal Empire for her first Princess Summit, Sunset Shimmer comes across a strange mirror hidden away in the empire with a strange pony in it that she could have sworn she's seen before.
A thousand years after banishing her beloved to the moon, Princess Twilight Sparkle will have to face the sins of her past as her student fights for their future.
1000 years ago, Princess Twilight Sparkle banished Princess Rainbow Dash to the heavens. Now, free of the darkness that corrupted her, she enlists the aid of Celestia and Luna, the mares that saved her, to help free her sister from her starry prison.