Small Gods by Terry Pratchett is the story of a dimwitted novice priest of the god Om, named Brutha, with an eidetic memory who becomes a prophet rather against his will. Unfortunately when Brutha meets his god, Om happens to be trapped in the form of a tortoise and is almost powerless. It's up to Brutha to help Om figure out why this happened and to help restore his god to his former glory. In the process Brutha learns the truth about his religion and that much of what he had been taught was false.
This is a very funny religious satire. It made me grin a lot and at times even laugh aloud. I'd definitely recommend this book to Discworld fans as well as anyone who enjoys British humor, provided you aren't sensitive about the subject matter.