The Wee Free Men: (Discworld Novel 30) Terry Pratchett
EVERY LAND NEEDS ITS OWN WITCH . . .
Up on the Wold, there's a monster in the river and a headless horseman in the drive. And now Granny Aching has gone, there's only young Tiffany Aching left to guard the boundaries. To stop . . . things getting through.
It's her land. Her duty.
But it's amazing how useful a horde of unruly pictsies can be - as long as they are pointed in the right direction and can stop fighting each other first . . .
FROM MASTER STORYTELLER TERRY PRATCHETT