The Screwtape Letters is a book written during the time of World War 2 by CS Lewis (author of the Narnia Chronicles). CS Lewis & J.R.R Tolkien were buddies.
Screwtape is the name of a ranking military/spy-type official in the service of the devil (or the Father below) as they call him. The cunning Screwtape is the mentor of his younger nephew Wormwood, an inexperienced, useless devil. Wormwood has 1 job – to tempt and distract a young man (called the Patient) away from God (called the Enemy). The Screwtape letters is a series of letters where Screwtape advises Wormwood on how to best undermine “the Enemy’s” work in the life of “the Patient”.