What was the title of C.S. Lewis’s 1942 book based on imagined letters from a demon?

C.S. Lewis’s 1942 book based on imagined letters from a demon is The Screwtape Letters.

The book consists of correspondence from Screwtape, an experienced demon, to his younger nephew Wormwood. Screwtape offers advice about tempting a human subject, while Lewis uses the reversed perspective to examine pride, distraction, self-deception, resentment, and spiritual growth.

The unusual format lets Lewis discuss Christian ethics without presenting the advice as a direct sermon. The demonic narrator routinely misunderstands or distorts goodness, so the reader is expected to infer the moral lessons from the contrast between demonic language and Christian belief.

The book was first published in Britain in 1942 and became one of Lewis’s most widely read religious works. It is sometimes confused with The Great Divorce, another Lewis book using imaginative fiction to explore spiritual choices, but that work takes the form of a journey between heaven and hell.