Which C.S. Lewis book presents Christianity through conversations between a senior and junior devil?

The Screwtape Letters presents Christianity through fictional advice from a senior devil to a junior devil. C.S. Lewis wrote the book as a series of letters from Screwtape to his nephew Wormwood.

The letters discuss temptation, distraction, pride, fear, pleasure, and everyday human habits from the perspective of Hell’s bureaucracy. That reversed viewpoint lets Lewis explore Christian moral psychology without presenting the book as a conventional sermon or theological treatise.

Lewis first published the work in book form in 1942. Readers sometimes remember Screwtape as the junior tempter, but Screwtape is the experienced uncle giving instructions, while Wormwood is the apprentice assigned to influence a human “patient.”