A Hat Full of Sky, which is Terry Pratchett's 32nd Discworld novel and second featuring Tiffany Aching, takes place two years after the events of Wee Free Men (where our heroine saved Chalk from the Queen of Fairyland). Now at 11 years old, Tiffany is leaving the Chalk to learn witching from Miss Level, a singularly talented witch (and a in-joke on British A Levels). Meanwhile, changes are afoot for the Nac Mac Feegle clan as well, as the new Kelda, Jeanine of the Long Lake, is bound and determined to bring her blue boys into the current century by telling them they must learn to read and write. Of course, for the Pictsie leader, the idea of doing what the Kelda requests is filled with dark implications. Especially since, as Rob Anybody notes, "Words stay." But before this can begin, the Nac Mac Feegle realize an ancient evil called the hiver is stalking their "wee big hag." The hiver is a entity attracted to power and Tiffany is certainly becoming a powerful witch, so Rob and his men (with reluctant blessing of Jeanine) set out to protect her.
What seems to have made Terry Pratchett such a great writer was his innate ability to give you lessons -like talking about bravery and the human condition- while making you laugh. Tiffany -if I can make a wild assumption- is probably based on Pratchett's daughter and she is turning out to be a fully realized character; she's a bit precocious, smart and very likable (which I assume his daughter to be). She could be what us folks really hope to be. Then there is the Nac Mac Feegle, characters written to be the comic relief (and brilliantly), but they have some great wisdom that can also be very moving. So much like his other fantasy novels, these Young Adult tales (and I'm unsure why I kind of feel kind of insulted they're categorized that way) can be read and enjoyed by folks of all ages.