Which C.S. Lewis book presents a demon’s advice to his nephew Wormwood?

The C.S. Lewis book presenting a demon’s advice to his nephew Wormwood is The Screwtape Letters.

The book is a series of fictional letters from Screwtape, a senior demon, to Wormwood, a younger tempter assigned to influence a human being. Lewis uses the imagined correspondence to discuss temptation, pride, distraction, repentance, prayer, and the moral habits of ordinary life.

The work first appeared as a serial in the Anglican newspaper The Guardian in 1941. It was published in book form later that year. Its unusual viewpoint reverses the expected perspective: readers hear demonic advice while inferring the Christian ideas Lewis is defending.

The Screwtape Letters is often grouped with Lewis’s works of Christian apologetics, but it is written as imaginative satire rather than as a direct theological treatise. It should not be confused with Mere Christianity, which developed from radio talks and presents arguments in a more straightforward nonfiction form.