In "Hogfather", Terry Pratchett takes a satirical swipe at Christmas and childhood beliefs, throwing in Santa Claus, the tooth fairy, easter bunny etc. in this hilarious tale.
In the Discworld, the Hogfather visits all the good children on Hogswatch eve with presents for all. However, this year, the Auditors who keep reality in check, have commisioned an assassin to take out the Hogfather and thus fix what they see as a glitch - the Hogfather exists if you belive but not if you don't...thus a glitch. Or something. Anyhoo...Death steps in to fill in whilst the Hogfather is gone, with a pillow stuffed up his red suit and false beard whilst his grandaughter Susan tries to track down the mystery of what happened to the Hogfather before it is too late.
Pratchett books are somewhat hard to describe in terms of plotting because in many cases they are so out there you just have to read to get what's going on. Even so, these books are nothing short of hilarious and this one is no exception. It was also recently made into a movie (albeit of a somewhat low budget) which was much more entertaining than I expected it to be and worth checking out if you can find it.
I loved this book, as I have loved pretty much all of Terry Pratchett's other books. If you're a fan, then you'll not be disappointed. If you've never read one before, the expect lots of quirky humor, dry wit and satirical lampooning of our own beliefs and lots of just plain fun. Highly recommended.