In The Screwtape Letters Lewis writes a series of fictional letters reporting to be from a demon named Screwtape to his nephew Wormwood. In these he is instructing him how to tempt the man to whom he was assigned in order to bring about his ultimate damnation. This is not simply an interesting fiction read though. As you go through the whole course of this man's life in Screwtape's letters you will both entertained and educated. It teaches you some important truths about spiritual warfare in the form a brilliantly written story.