This document provides a summary and analysis of the use of irony in C.S. Lewis's book "The Screwtape Letters". The book is composed of letters between Screwtape, a mentor demon, and his nephew Wormwood. Screwtape advises Wormwood on how to tempt his human "patient" away from God. The letters utilize satire and irony, such as referring to God as deceitful and the demons as helping their patients, which subverts the normal meanings of these terms. The 19th letter in particular reveals Screwtape's true cruel and manipulative nature behind his friendly mentoring tone. In short, the document analyzes how Lewis employs satirical irony through the demon