Pioneer (Utah's Online Library). It also includes Screwtape Proposes a Toast, and is read by Ralph Cosham (who does an excellent job).
A masterpiece of satire, this classic has entertained and enlightened
readers the world over with its sly and ironic portrayal of human life
and foibles from the vantage point of Screwtape, a highly placed
assistant to "Our Father Below." At once wildly comic, deadly serious,
and strikingly original, C. S. Lewis gives us the correspondence of the
worldly-wise old devil to his nephew Wormwood, a novice demon in charge
of securing the damnation of an ordinary young man.
Even though I can't always give 100% attention to an audiobook, I thoroughly enjoyed Screwtape's letters to Wormwood, and his toast to fellow demons. There was so much food for thought. Many of the demons "tricks" are things/attitudes that I've seen often in my life. This is definitely a book to read (there were so many parts I would have marked).