Fairy Tale, Historical Fiction, Mystery
Briar Rose isn't a straightforward fairy tale: instead, it's a retelling of Sleeping Beauty folded into a story about the Holocaust. (Yep, that's where the historical fiction part comes into play. The characters are fictional, but the situations they are in really happened in the 1940s.)
Then, all those stories are nestled like a bug in a rug inside a more-or-less contemporary story about an American family living in rural Massachusetts, which an alien warlord is telling to his daughter as a bedtime story.
We're kidding about the alien warlord. There isn't one—though maybe there should be. Hey, Jane Yolen, did you ever think of that?
Also worth noting: Briar Rose is a mystery story. Gemma doesn't provide Becca with a list of names and addresses; she more or less blurts out "swear to me you'll find my secret castle," and then dies. Becca Scooby-Doos herself all the way to Poland, where Gemma's life story finally comes into focus. Sherlock couldn't have done it better.