The Goose Girl is a re-telling of the Grimm Brothers tale. Anidori-Kiladra Talianna Isilee is the Crown Princess of Kildree, the first born who will inherit the throne. At least, that's what is supposed to happen. Legally.
Her mother decides otherwise, packing Ani off to be married to the Crown Prince of the next country over, partly because the Queen is trying to forge an alliance that will stave off an unnecessary war, and partly because she doesn't think that Ani has what it takes to rule. Proper queens don't understand the language of birds. They also don't ride stallions. Or communicate with them.
While Ani knows in her heart that the Queen is right--she wouldn't really make a ruler that her superstitious countrymen would take pride in--she is understandably unhappy about it. But, being the obedient daughter that she is, she sets off for Bayern with her lady-in-waiting and a large traveling company.
I'm not going into the rest of it--how Ani becomes Isi the Goose Girl, whether or not she ever claims her rightful place--if you know the old story, you know the basics. Shannon Hale has done what Gerald Morris has done with the Malory stories--she's expanded and explained while staying true to the original. As I neared the end, I had to force myself to slow down over and over again--I wanted to skim just so I'd know how things turned out. I'm looking forward to reading Enna Burning.