Sunset Shimmer is forced to reconsider her future as a citizen of Earth rather than as a student of magic in Canterlot, and part of giving up her life in Equestria means giving up her original form forever, triggering a bout of intense homesickness in the ex-unicorn.
After an encounter with an unknown magical source, Sunset's greatest wish is granted. She is once again a unicorn, back in her original body.
Just one problem.
Actually, several.
She's lost, she can't be seen by anyone but her friends, and she stands at a solid three feet tall.
Oh yeah. And her magic isn't working.