Jaclyn Moriarty's A Corner of White
I'm rereading this because the third volume comes out pretty soon, and also because it's great, and also because I've forgotten a lot of the details since the last time I read it! It was almost like reading it for the first time again (though I did remember the big end reveal). I love that Moriarty has created two connected worlds here, populated with vibrant and funny and interesting characters, and even managed to throw in a couple of little mystery elements. Totally, totally holds up.