Although most famous for his Narnia series, a Christian allegory for children, C.S. Lewis (that's "Clive Staples Lewis" to you young man!) also wrote plenty of explicitly religious books for adults. I came across "The Screwtape Letters" in a reading list prepared by philosophy professor Dr. Robert Kreeft (a devout Catholic). It was a book that, as C.S. Lewis himself said, "wrote itself" after he came up with the key idea. That key idea was to create an epistolary novel in which a demon ("Screwtape") gives advice to his tempter-in-training nephew ("Wormwood"). It's a marvelous conceit and one which C.S. Lewis executes brilliantly. I would have given this one 5 stars but it does drag a bit in some parts. But on the whole, it's a delightful little book that is over too soon. The audiobook narration by Joss Ackland is pitch-perfect and makes this a perfect road-trip pick. I'm sure I'll be reading the text version at some point.