Which C.S. Lewis book was written as a series of letters from a senior demon to a junior demon?

The Screwtape Letters is the C.S. Lewis book written as letters from a senior demon to a junior demon.

Published in book form in 1942, the work consists of advice from Screwtape to his nephew Wormwood. Wormwood has been assigned to influence a human being, while Screwtape comments on methods of temptation and on the habits that can weaken a person’s moral and spiritual attention.

Lewis’s unusual narrative method depends on irony. The demons praise actions and attitudes that readers are meant to recognize as destructive, such as vanity, envy, resentment, and obsessive concern with trivial matters. Because the advice is written from a demonic viewpoint, the book’s Christian argument is presented indirectly.

The work is sometimes confused with Mere Christianity, which grew from wartime radio talks, or with The Problem of Pain, a direct theological discussion. Neither uses the demonic-letter format. The Screwtape Letters is the distinctive epistolary satire.