Perelandra by C.S. Lewis

This book replays the story of Eve's temptation in Genesis on the planet Venus. But instead of leaving the serpent to his own devices, this time good gets an advocate in the form of Dr. Ransom who has been sent to Venus (or Perelandra, in Lewis's system) to make a case for Maleldil (that is, God and goodness). Lewis creates a beautiful world, as always, and makes a lovely case for goodness and virtue. Indeed, it's one of the best clarifications of the nature of original sin that I've ever read. For both its literary and its philosophical merits, I strongly recommend this book.