Which 1942 C.S. Lewis book presents Christian apologetics through a series of letters from a senior demon?

The Screwtape Letters is the 1942 C.S. Lewis book presented as advice from a senior demon.

The book consists of letters from Screwtape, an experienced demon, to his inexperienced nephew Wormwood. Screwtape offers strategies for tempting a human “patient,” while the reader must infer Christian moral teaching from the demonic perspective.

Lewis published the work in 1942, during the Second World War. Its epistolary form made abstract discussions of temptation, pride, distraction, and spiritual self-deception accessible through irony and satire.

The book is sometimes mistaken for straightforward horror or for a conventional theological treatise. It is better described as Christian apologetics and satire. Lewis later wrote a preface explaining that the demonic viewpoint had become unpleasant to sustain, and he cautioned readers against treating the letters as a literal handbook of demonology.