I Shall Wear Midnight by Terry Pratchett (Discworld series #38)
I thoroughly enjoy the "Tiffany Aching" series that takes place amongst Terry Pratchett's Discworld books, but not so much because of the main character, Tiffany Aching. The real enjoyment in reading these books for me are the Nac Mac Feegles, miniature pixies (for lack of a more accurate designation) who live to steal, fight, and kill anyone whom they consider a threat, an annoyance, or who simply finds themselves in the Feegles' line of sight when they're in need of a cure for boredom. They speak with a Scottish Brogue, believe that the Discworld is a heaven and that they must have been very good to have been sent there, and are fiercely loyal to Tiffany Aching, a teenage witch who has reciprocated their loyalty in the past.
In this, the fourth book in the series, Tiffany, who is finally starting to feel comfortable with her role and abilities as a witch, finds herself up against a force or presence that she inadvertently woke up at the conclusion of Wintersmith.