This is a very funny book, but not recommended for anyone who's likely to be upset by some light-hearted blasphemy!
In his later novels, Gore Vidal (who died in 2012, aged 86) was particularly interested in the possibilities of time travel for speculative fiction; changing the past. This book is a particularly spectacular example. Someone has been going back in time and interfering with the crucifixion! The narrator and hero, who is Timothy, St. Paul's young assistant, is visited by time travellers and tasked with sorting this out and then writing a true account of what happened, since all existing gospel texts have been hacked into and corrupted. Amongst other discoveries, he learns that Jesus was grotesquely overweight, which comes as a shock - though why shouldn't he have been very fat: there's no physical description of Jesus anywhere! But then the question emerges: is this the real Jesus?
Things get more and more complicated, but then the last pages bring the finest denoument I have ever come across in a novel. You think: of course! that's what's been happening! why didn't I spot it earlier! No reader should ever cheat and look at the last pages before reaching them!