A Hat Full of Sky by Terry Pratchett

In this book Tiffany Aching leaves home to train as a witch, but must face the hiven, an enemy which can get inside her head and turn her downright nasty. I liked the second half of this book, which featured Tiffany thinking for herself on how to finally defeat the hiven and what it means to be a witch better than the first, where she was more passive. The second half also has a good appearance by Granny Weatherwax, who is as delightful as always. Like the other young adult Discworld books, I don't think the humor, parody, and satire work as well here as it does in the adult books.