Which C.S. Lewis book presents a fictional debate between a senior demon and his junior nephew?

The Screwtape Letters presents a fictional correspondence in which the senior demon Screwtape advises his inexperienced nephew Wormwood on tempting a human. C.S. Lewis published the book in 1942 during World War II.

The letters are written from a demonic perspective, so their ironic praise of selfishness and distraction exposes those habits as moral dangers. Lewis used the epistolary format to discuss Christian ethics without presenting a conventional sermon. The unnamed human is called “the Patient,” while God is sarcastically described as “the Enemy.”

Lewis later said the book had not been enjoyable to write because sustaining the demonic viewpoint was psychologically unpleasant. Despite that, it became one of his most popular works and has remained in print in many languages.