I Shall Wear Midnight: (Discworld Novel 38) by Terry Pratchett
As the witch of the Chalk, Tiffany Aching performs the distinctly unglamorous work of caring for the needy. But someone - or something - is inciting fear, generating dark thoughts and angry murmurs against witches.
Tiffany must find the source of unrest and defeat the evil at its root. Aided by the tiny-but-tough Wee Free Men, Tiffany faces a dire challenge, for if she falls, the whole Chalk falls with her . . .
THE FOURTH BOOK IN THE TIFFANY ACHING SEQUENCE