What is the name of C.S. Lewis's 1942 book presented as letters from a senior demon?

C.S. Lewis's 1942 book presented as letters from a senior demon is The Screwtape Letters.

The book consists of fictional correspondence from Screwtape, an experienced demon, to his junior nephew Wormwood. Screwtape offers advice about tempting a human patient, while Lewis uses the reversed viewpoint to examine pride, distraction, resentment, and self-deception.

The work first appeared in book form in 1942, during the Second World War. Lewis had already developed a version of the idea for a series of newspaper pieces, and the epistolary format gave him a way to discuss moral and spiritual habits indirectly. The satire depends on readers recognizing that the demons’ advice is meant to expose human weaknesses rather than praise them.

The Screwtape Letters is sometimes confused with Lewis’s nonfiction apologetic books. Unlike Mere Christianity or The Problem of Pain, it makes its argument through imaginative fiction and demonic irony.