Which C.S. Lewis work is a 1942 allegory about a senior demon advising a junior tempter?

The C.S. Lewis work about a senior demon advising a junior tempter is The Screwtape Letters.

Published in book form in 1942, The Screwtape Letters is structured as a series of letters from Screwtape, an experienced demon, to his inexperienced nephew Wormwood. Screwtape advises Wormwood on how to tempt a human patient away from Christian faith and moral responsibility.

Lewis uses the demonic point of view satirically: the advice exposes self-deception, distraction, vanity, resentment, and other ordinary weaknesses. The reader is expected to reverse the demons’ perspective and recognize the spiritual and psychological dangers being described.

The book was first published during World War II, when Lewis was already becoming known through his broadcasts and apologetic writing. Its unusual epistolary form makes it distinct from his more direct theological works.