Which C.S. Lewis book presents the fictional demon Screwtape giving advice to a junior tempter?

The C.S. Lewis book in which the demon Screwtape advises a junior tempter is The Screwtape Letters. Lewis published the work in 1942.

The book is structured as a series of letters from Screwtape, an experienced demon, to his nephew Wormwood. Their subject is the attempted spiritual corruption of a human patient. Lewis reverses the usual moral viewpoint by presenting temptation, pride, distraction, and self-deception through the imagined bureaucracy of Hell.

The unusual format lets Lewis criticize human habits without making the narrator a reliable moral guide. Readers are meant to infer the author’s Christian argument from Screwtape’s distorted advice. The book became one of Lewis’s most popular works and was written during the Second World War.

Screwtape is not the human protagonist, and Wormwood is not the name of the patient. The title refers to the letters themselves, while the fictional correspondence provides the entire structure of the book.