Which C.S. Lewis book argues for Christianity through a fictional dialogue between a demon and his nephew?

The Screwtape Letters argues for Christianity through fictional letters from a senior demon to his nephew. C.S. Lewis published the book in 1942, during the Second World War.

The senior demon, Screwtape, advises the younger Wormwood on how to tempt a human being. Lewis presents the advice ironically: the demons praise distraction, pride, resentment, and self-deception, while readers are expected to recognize the moral danger in those habits.

The book’s epistolary form lets Lewis discuss Christian ethics indirectly. Instead of giving a conventional sermon, he reverses the viewpoint and describes human weaknesses as opportunities for demonic influence. That satirical approach made the book both accessible and unsettling.

Mere Christianity is also a major Lewis defense of Christianity, but it developed from radio talks and is not a fictional correspondence. The Great Divorce and Till We Have Faces are different works as well, so the demon-and-nephew structure identifies The Screwtape Letters.