The Power and the Glory
This novel, originally published in 1940 was criticised by the Vatican at the time. Set in the Mexico of the 1930s it follows an unnamed 'whisky-priest' who is evading the government forces who were brutally supressing the Roman Catholic church, forcing priests to marry and give up their religious clothing. He travels the country hearing secret confessions and performing mass but this is also a man who drinks heavily, is gluttonous; as much a sinner as a saint. And that of course is what makes the book a classic, regarded by many as being Greene's masterpiece. That said, we could very easily have added The End of the Affair to this list too.