Many, many years after the third world war -- which evidently happened some time in the late 1950s -- the Albertian Order of Leibowitz, a Catholic monastery, guards the remains of human knowledge in the American desert against a new Dark Age.
The book's structured in three parts, set hundreds of years apart, with rather jolting transitions between parts. The overall effect is rather self-consciously arty. It's easy to find reviews that rave about this book, but I'm rather less convinced; the world the author has built is interesting, but he doesn't stay in one place long enough for the reader to get a coherent picture of what's going on -- and by the time we've started to care about the characters, they're all dead and we're reading about someone else.
Nice idea; shame about the execution, I think.