Which C.S. Lewis book presents an imagined debate about Christianity between a senior and junior demon?

The Screwtape Letters is the C.S. Lewis book presented as correspondence between a senior and junior demon.

The senior demon, Screwtape, writes letters to his nephew Wormwood, offering advice on how to tempt a human being away from faith and virtue. Lewis uses the inverted viewpoint to examine pride, distraction, vanity, resentment, and other weaknesses that can affect ordinary life.

The work was first published in book form in 1942, after appearing in the Anglican newspaper The Guardian. Its unusual structure makes moral and theological ideas accessible through satire rather than through a conventional sermon or essay.

Readers sometimes confuse The Screwtape Letters with Mere Christianity because both discuss Christian belief and were written for a broad audience. Their forms are different: The Screwtape Letters is fictional correspondence from a demon’s perspective, while Mere Christianity develops arguments from radio talks and apologetic writing.