Which 1942 C.S. Lewis book is written as letters from a senior demon?

The Screwtape Letters is the 1942 C.S. Lewis book written as letters from a senior demon.

The book presents a series of fictional letters from Screwtape, an experienced demon, to his inexperienced nephew Wormwood. Screwtape offers advice on tempting a human patient and keeping him away from Christian belief and moral reform.

Lewis uses irony by making demonic advice reveal the weaknesses of pride, distraction, resentment, and self-deception. The book is therefore structured as satire rather than as a conventional novel with scenes narrated by a human protagonist.

The letters first appeared in the Anglican newspaper The Guardian in 1941 before being collected in book form in 1942. Readers sometimes confuse Screwtape with Wormwood, but Screwtape is the senior adviser and correspondent; Wormwood is the junior tempter receiving the letters.