Which C.S. Lewis book collects his fictional letters from a senior demon advising a junior tempter?

The C.S. Lewis book that presents letters from a senior demon to a junior tempter is The Screwtape Letters. Lewis published it in book form in 1942.

The fictional correspondence is written by Screwtape, an experienced demon, to his nephew Wormwood. Screwtape offers advice on how to influence a human subject away from faith, virtue, and clear thinking. Lewis uses the reversed perspective to examine temptation, pride, distraction, bureaucracy, and self-deception.

The work first appeared as a series of letters in the Anglican newspaper The Guardian. Lewis later collected the letters into a book. The format allows him to discuss moral and theological ideas through satire rather than direct instruction.

The Screwtape Letters is sometimes confused with Mere Christianity because both grew from Lewis’s Christian broadcasts and public religious writing. They are different works: Mere Christianity presents arguments and explanations, while The Screwtape Letters uses an imagined demon’s correspondence as its narrative device.