Which 1942 C.S. Lewis book uses the fictional demon Screwtape as its narrator?

The 1942 C.S. Lewis book narrated through the fictional demon Screwtape is The Screwtape Letters.

The Screwtape Letters is a satirical Christian novel presented as a series of letters from Screwtape, a senior demon, to his inexperienced nephew Wormwood. Screwtape offers advice on tempting a human being, whom he calls “the Patient.” Lewis uses the demonic viewpoint to expose self-deception, distraction, pride, and other moral weaknesses.

The book first appeared in serial form in the Anglican newspaper The Guardian before being published as a volume in 1942. Its unusual viewpoint can cause readers to mistake Screwtape for the human protagonist, but he is the letter writer and an imaginary demon. The work is fiction and satire rather than a literal handbook of theology.