Twilight Sparkle has been studying the mechanics of flying recently, as per her personal assignment of reading every book in her library. Studying the differences between birds and pegasi, she realizes something. Pegasi shouldn't fly. It's scientifically impossible. Continuing her studies, she begins using Rainbow Dash as a test subject and begins studying the stuff that makes flying, magic, and earth ponies' working with the dirt possible. Alicorn. Discovering that taking alicorn from a pegasus and giving it to a unicorn will create temporary wings, she begins to wonder about the Royal Sister Alicorns, and how they get their wings and horn.

Contacting the Princess about her studies, she learns Celestia and Luna may have a big secret under their wings, and it sure as Tartarus isn't legal.