The Wee Free Men; A Hat Full of Sky - Terry Pratchett

Tiffany Aching is spotted as a potential witch at the age of 9, by Miss Tick, a Witch-Finder (that is, a witch who finds girls with Witch potential), who sees to it that Tiffany begins her magical education, not at a Hogwarts-style school, but by becoming an apprentice to different individual witches for a period of time. She is the kind of child who, after reading in her book of stories that Jenny Greenteeth has eyes the size of soup plates, measures a soup plate to check the size; she knows the meanings of lots of words since no one has ever told her that you’re not meant to read the dictionary like a novel. She’s also the kind of child who, hearing stories about the "wicked old witch", wonders "Where’s the evidence?"

In The Wee Free Men Tiffany encounters the fairy tale monster, Jenny Greenteeth, whom she wallops with a cast-iron frying pan, and sends on her way, because a monster has no business being in her river. She then meets Miss Tick, who tells Tiffany that "an incursion of major proportions" is about to take place; in other words the Queen of the Faerie is about to invade Tiffany's world. This being Terry Pratchett, we’re not talking about Tinkerbell fairies, so Miss Tick sets off to fetch help as she does not believe that either of them are capable of dealing with the Queen. Unfortunately, Tiffany's three year old brother, Wentworth, is kidnapped by the Queen, who takes him back to Fairyland. Fortunately, Tiffany finds herself some indomitable allies when she is temporarily made the Kelda (leader) of the Wee Free Men (aka the Nac Mac Feegle), a clan of 4 inch high blue men with an over-aggressive attitude (they love fighting, stealing and drinking, preferably all at once), but astonishing loyalty. They assist Tiffany in entering Fairyland and in her encounter with the Queen.

In the sequel, A Hat Full of Sky, Tiffany goes off into the mountains to stay with Miss Level to be her apprentice so she can learn to be a witch. Unfortunately, just before she leaves the Chalk (where she lives), she attracts the attention of a "hiver", a bodiless creature that likes to inhabit minds until the owners of those minds go mad and die. Despite the fact that she's no longer their Kelda, several of the Nac Mac Feegle go after Tiffany, disguising themselves as a human by dressing up in stolen clothes (and a stolen beard) so that they can get the stagecoach up into the mountains. However, the hiver has already possessed Tiffany's mind and they find themselves forced to go after Tiffany (being otherworldly creatures, they're able to enter Tiffany's mind via her dreams). Tiffany manages to free her mind from the hiver, but it hangs around, wanting her power for itself. I'm not going to tell just how Tiffany chooses to deal with this frightening and threatening creature, except to say that she does so in a remarkably mature and unselfish manner. A Hat Full of Sky is a compelling look at the power of storytelling, a topic to which Pratchett returns again and again in his books.