The first book in the Tiffany Aching trilogy, the Discworld YA books. (Helps a bit if you've read some of the Witch books first.) I was at first wary because his first venture in YA did not impress me. This is much better.
Tiffany Aching is the youngest daughter of seven, with a younger brother, on a sheepfarm on the Chalk. The witch Miss Tick is watching when she is warned by a Nac Mac Feegle (a small but extremely fierce group of the -- ehem -- Fair Folk) and, using a frying pan, deals with a Jenny Greentooth. But Miss Tick can only give Tiffany a few warnings -- it's on the Chalk, which weakens her -- and Tiffany has to deal with an incursion from Fairyland, which is not half so pretty as Victorians made it out to be. And the Baron's son had already vanished. When the kelda of the Nac Mac Feegles brings her in to hold that position until the problem's been dealt with, she is even more bound in.
It involves snow, hounds with eyes of flame, a dangerous ball where the farther off dancers are not that clear, the time Tiffany's grandmother taught a dog not to kill sheep, Jolly Sailor tobacco, swords that glow in the presence of lawyers, a talking toad, and much more.