The Wintersmith book is the third in the Tiffany Aching series. I have read the first two, and I really enjoyed them as well. The difference between this series and the regular Discworld novels is that the story is in no way about Ank Morpork. There is also a set of little tiny blue people who are known as the Mac Nac Feegles.
In this particular story, 13 year old Tiffany gets the Wintersmith to fall in love with her because she accidentally dances with him during the dark morris dance. This dance is done to transition fall to winter. Throughout the story she must try to prevent the Wintersmith from giving the world an eternal winter, and she also has to learn about herself and the world.
I really like this series. I think that Terry Pratchett understands people and how they think and is able to present truths about the world in a funny way. This story is enjoyable for adults and young people. Anyone over the age of 11 should enjoy this story. I give it five stars! However, you should read the first two stories, The Wee Free Men and A Hat Full of Sky, first.