Things have been going well for Sunset Shimmer since the Friendship Games. She's on good terms with the students at Canterlot High School, she has a close circle of friends she can depend on, and most of all, she now has a new friend and research partner in the form of the human world's Twilight Sparkle. With a brand new avenue in magical research now open to her, not even the prospect of her upcoming birthday can get in the way of her hope for the future.

Then her latest experiment blew up in her face.

Reduced to a mare in a child's body, Sunset has to find a way to reverse what she's done and return to what qualifies as normal in this world. But in a world where magic was a fairy tale until a few months ago, things are going to be more than a little difficult on that front. And as she struggles to maintain her adult mind against the immaturity of her current form, her friends are faced with the possibility that they may lose their friend forever.