This story is a sequel to Fluttershy, Royal Game Warden (?)
Ever since Rarity was a wee filly, she has always fantasized about the life of the nobility. The inestimable glamour! The fabulous balls and galas! The magnificent castles! Even after running roughshod into the very worst of highborn snobbery at the Gala, that little foalish tingle keeps dragging her mind back to that particular whimsy in the quiet times.
Incidentally, Luna needs some poor gullible idiot she can ennoble before throwing them into the very foulest political cesspit in Bitaly on a wild-goose chase for nine million bits. How convenient!
Reading the previous story is highly recommended, not only because this one won't make much sense without it, but also because it's a 100% certified banger. Obviously.