Which C.S. Lewis book presents Christianity through letters from a demon to his nephew?

The Screwtape Letters presents Christianity through letters from a demon to his nephew. C.S. Lewis published the book in 1942.

The fictional senior demon Screwtape writes instructional letters to Wormwood, a junior tempter assigned to influence a human patient. The letters reverse the usual moral viewpoint: readers hear demons discuss temptation, distraction, pride, and spiritual failure as if they were professional techniques.

Lewis used this satirical device to examine Christian ethics and ordinary human behavior. The work is not a conventional narrative with a continuous sequence of scenes; its structure is an exchange of advice from an experienced tempter to an inexperienced one.

The book first appeared in serialized form in the Anglican newspaper The Guardian before being published as a volume. Lewis later wrote a final piece, “Screwtape Proposes a Toast,” which was published separately and then commonly included with the letters.