Sunset Shimmer doesn't remember what happened at the last night's party. And worse yet, she can't remember just which one of the Twilight's she slept with
Sunset has had the same jacket ever since she came to Canterlot High. Rarity and the girls want to treat her to some new clothes, but some things are too important to be replaced.
When Sunset sees herself as an alicorn in a magical mirror, she goes looking for answers, eventually going through the mirror into another world. Some things are better left alone though, as she finds herself trapped in the other world as a child.