Which C.S. Lewis work presents an imagined correspondence between demons?

The Screwtape Letters presents an imagined correspondence between demons.

Published in book form in 1942, the work consists of letters from Screwtape, a senior demon, to his inexperienced nephew Wormwood. Screwtape offers advice about tempting a human patient, while Lewis uses the reversed viewpoint to examine pride, distraction, resentment, habit, and spiritual self-deception.

The device is satirical: readers are expected to infer the author’s moral perspective from the demons’ advice rather than receive a conventional sermon. Lewis later said the format was difficult to sustain because writing in the voice of a demon affected his mood.

The book became one of Lewis’s most widely read works. It is sometimes described as a novel, but it is more precisely a fictional series of letters. Its named characters are demons, while the human target remains unnamed.