Sunset Shimmer was, a long time ago, Princess Celestia's student. The one who would free her sister from her imprisonment on the moon, and complete a variety of prophecies. When Sunset's ambition made her fling herself into a mirror, something went... wrong.
In the aftermath of several crises, Nightmare Moon's Equestria is a fractured country. The bindings of prophecy have been broken, and the world is reeling in the aftermath. Can Sunset Shimmer succeed where she failed before? Can she pick up the torch left behind by Celestia's 'replacement' for her?
Probably not, but come Tartarus or high water, she's not going to let the world pass her by.