The novel consists of 31 letters written by a devil named Screwtape to his nephew, a young devil named Wormwood. The author, C.S. Lewis, notes that he has no intention of explaining how he came to acquire these letters.
In the early letters of the book, Screwtape responds to the news that Wormwood is busy trying to tempt a young man, the patient, to move away from God—the Enemy, as Screwtape calls him—and embrace sin. Screwtape gives Wormwood advice on how to influence the patient in various small ways, thereby encouraging the patient to move away from God and toward “Our Father,” Satan.
Screwtape advises Wormwood to prevent the patient from thinking whenever possible, since reason will only encourage the patient to accept Christianity with greater fervency. Wormwood should try to prevent the patient from thinking about the history of Christianity, and instead influence the patient to focus excessively on the ugliness and imperfection of his peers and of family, especially his mother. In this way, Wormwood can encourage the patient to focus too exclusively on vice, imperfection, and the material realm, and reject piety, perfection, and the abstract moral realm.
Wormwood reports to Screwtape that a war (World War II) has broken out in Europe, prompting Screwtape to send Wormwood a series of letters on fear, violence, and bravery. Screwtape explains that war can be good or bad for the devils’ cause. It’s good in the sense that it fills people with fear and makes them turn to sin and sensual pleasure, but it’s also bad because it encourages people to think seriously about death, and therefore behave morally. Screwtape explains to Wormwood that whether the patient becomes a patriot or a pacifist, if he is extreme in his beliefs then his behavior will be sinful—extremism of any kind, except extremism for God, is a sin.
Wormwood writes to Screwtape, proud that the patient is “losing his religion.” Screwtape angrily reminds Wormwood that people are always moving between periods of depression and disappointment and periods of happiness—unfortunately, periods of depression are actually good for God, because if people can continue to worship God during this time, then it makes them nearly impossible to corrupt in the future. Screwtape adds, grudgingly, that God loves humanity and wants them to be rewarded for their virtue in Heaven. He also notes that modern European society has an irrational prejudice in favor of the new and of fashion—this encourages people to abandon Christianity simply because it’s old-fashioned, a great help to devils.
Screwtape learns that the patient has befriended a married couple that regularly mocks Christianity and celebrates the importance of progress. Screwtape tells Wormwood to use this development to his advantage: he should encourage the patient to spend more time with the couple, until the couple’s beliefs gradually become his own. Screwtape warns Wormwood that although he is successfully corrupting the patient, he must be careful not to corrupt him too quickly, for fear that the patient will realize that he is sinning and return to the church.
In his next letter, Screwtape reveals that Wormwood has failed to corrupt the patient—in fact, he has allowed the patient to return to the church. Wormwood allowed this to happen, Screwtape angrily explains, by letting the patient experience pleasure. Pleasure, Screwtape shows, is always dangerous for devils, since God is its creator. While some kinds of pleasure can be sinful, it’s only sinful because of the quantity of pleasure being demanded.
There is a lull in the war in Europe, filling the patient with fear and anxiety. During this lull, Screwtape addresses a wide variety of questions Wormwood has raised about humanity, virtue, and sin. Screwtape notes that humans corrupt themselves when they become “connoisseurs” of churches, and also notes with amusement that the Church of England has torn itself apart with hundreds of petty debates. He makes a thorough study of gluttony, concluding that it is just as gluttonous to fuss over small portions as it is to insist on large portions. Finally, Screwtape writes Wormwood a series of letters on the difference between love and lust, concluding that a weakness of modern European society is that is conflates these two things. As a result, millions of young couples marry out of lust, or, even worse, out of the mistaken belief that love is the only reason to marry someone. In reality, Screwtape writes, a marriage requires loyalty, respect, and hundreds of other virtues to work properly. Screwtape expresses his exasperation with the principle of love, noting that the goal of all beings is to fight and compete with other beings.
Wormwood writes Screwtape a letter in which he points out a contradiction in Screwtape’s reasoning—if God loves humanity, then how can it be true that the goal of all beings is to fight with other beings? Screwtape revises his own opinion, worriedly begging Wormwood not to show his letters to the “Secret Police,” which is responsible for punishing devils who commit heresy. Screwtape explains that God does not love humanity—on the contrary, his love for humanity is only a smokescreen to disguise his true, mysterious plan—a plan that no devil has ever understood.
In the following letter, Screwtape illustrates the fallacy in the patient’s belief that he is entitled to “free time.” On the contrary, the patient owes everything to God—his talent, his intellect, his body, and his time. Thus, it is sheer foolishness to suppose that one “deserves” anything at all. Screwtape speculates that God wants humans to reach the point where they can be aware of their talents and abilities, and yet also be fully aware that they owe everything to God.
Screwtape learns from Wormwood that the patient has fallen in love with a Christian woman, someone so virtuous that she makes Screwtape physically ill, and causes him to transform into a giant centipede. Screwtape smugly tells Wormwood that Wormwood’s attempts to report Screwtape to the Secret Police have failed, and that Wormwood faces a horrible punishment if he fails to corrupt the patient.
Now that the patient is with his lover, and is meeting her educated, Christian family, Screwtape advises Wormwood to appeal to the patient’s vanity and desire for the new. Modern humans, he explains, have an irrational desire for new things and fashions—this desire is ridiculous, he concludes, because new things aren’t inherently good or bad. When the patient begins courting his lover, Screwtape advises Wormwood to make the young couple think of love and nothing else. In this way, Screwtape explains, they will sacrifice their own happiness for one another’s sake, meaning that in the future, they will come to resent each other.
The war commences, and the patient is shipped off to fulfill his “duties.” Screwtape warns Wormwood that the patient could die in a state of virtue, before Wormwood has a chance to corrupt him. In general, he notes, humans are too afraid of death and too fond of life. Life and experience are good for devils, because over time, people begin to despair and become more prone to sin. Ironically, civilization values people who have had long lives and many experiences.
As the air raids on the patient’s community begin, Screwtape contemplates how to corrupt the patient. Wormwood’s goal, he writes, should be to encourage the patient to love his community and therefore hate all Germans. But this is difficult, since Wormwood runs the danger of encouraging the patient to feel more love and therefore be a more virtuous person. In the same way, Wormwood could encourage the patient to feel cowardice, but this would result in the patient feeling humility and therefore moving closer to God. In general, Screwtape admits, devils have a very difficult job—no matter how hard they try, mankind has a way of embracing faith and piety.
In his final letter to Wormwood, Screwtape greets Wormwood with false warmth and explains that the patient has died in an air raid. In his final moments of life, the patient “saw God,” and realized that no evil could ever corrupt him. Screwtape admits that he has no idea what God is trying to accomplish by loving humanity, and that he doesn’t know what awaits the patient in Heaven. He even expresses his desire to learn what lies in Heaven. Screwtape reminds Wormwood that he feels “the same love” for Wormwood that Wormwood feels for Screwtape. In the end, he reminds Wormwood that the penalty for failing to corrupt a human is being eaten alive—and Screwtape himself will be the devil to eat Wormwood.