I Shall Wear Midnight by Terry Pratchett

Tiffany Aching is almost sixteen and is now a respected witch across the Chalk. She is taken aback when the death of a local dignitary seems to spark off a burst of hatred and fear towards witches. Her investigation reveals the return of an ancient force of evil, which unleashes bigotry and invective even from mild-mannered people, even from Tiffany's oldest friends and allies. Fortunately the Nac…