That Hideous Strength is a 1945 novel by C. S. Lewis, the final book in Lewis's theological science fiction Space Trilogy. The events of this novel follow those of Out of the Silent Planet and Perelandra (a.k.a. Voyage to Venus) and once again feature the philologist Elwin Ransom. Yet, unlike the principal events of those two novels, the story takes place on Earth rather than in space or on other planets in the solar system.
The novel was heavily influenced by the writing of Lewis's friend Charles Williams and is markedly dystopian in style.

Plot summary

Mark Studdock — Protagonist; sociologist, obsessed with reaching the "inner circle" of any social environment.
Jane Tudor Studdock — Wife of Mark and clairvoyant dream-seer. Characters in "That Hideous Strength"

Francois Alcasan — "The Head", a French scientist executed for murder early in the book. His head is recovered by the N.I.C.E. and appears to be kept alive by the technology of man. In reality the Head has become a communication mechanism for the "Macrobes", the fallen eldila.
John Wither — Long-winded bureaucrat and "Deputy Director" of the N.I.C.E. He is the true leader of the N.I.C.E., and a servant of the Macrobes.
Professor Frost — A psychologist and assistant to Wither, he is the only other N.I.C.E member who knows the true nature of the Head, and of the Macrobes.
Miss/Major Hardcastle (a.k.a "The Fairy") — The sadistic head of the N.I.C.E. Institutional Police and its female auxiliary, the "Waips". Torture is her favorite interrogation method, and she takes special pleasure in abusing female prisoners.
Dr. Filostrato — An Italian physiologist, who has seemingly preserved Alcasan's head. However, he does not understand the Head's nature, believing it to be truly Alcasan. His ultimate goal is to free humanity from the constraints of organic life.
Lord Feverstone (Dick Devine) — The politician and aristocrat who lures Mark into the N.I.C.E. Feverstone was one of the two men who kidnapped Ransom in Out of the Silent Planet.
Reverend Straik — "The Mad Parson". He believes that any sort of power is a manifestation of God's will. This belief, along with other garbled beliefs, makes him a suitable candidate for introduction to the Macrobes. "He was a good man once", but became deranged by the death of his daughter.
Horace Jules — A novelist and scientific journalist who has been appointed the nominal Director of the N.I.C.E. His minimal understanding of science allows him to be unaware of the true nature of the Institute. He has a strong anti-clerical bias, and objects to Wither appointing "parsons" (such as Straik) to the Institute. The N.I.C.E. (National Institute for Coordinated Experiments)

Dr. Elwin Ransom — sometimes called "The Pendragon" or "Mr. Fisher-King". He alone communicates with the good eldila. Back from Perelandra, Ransom is a kingly figure among his small band of followers, and is usually referred to as the Director.
Grace Ironwood — The seemingly stern psychologist and doctor who helps Jane interpret her dreams.
Dr. Cecil Dimble — Another don, an old friend of Ransom and close advisor on matters of Arthurian scholarship and pre-Norman Britain.
"Mother" Dimble — Mrs. Dimble; She and Mr Dimble have no children, much to their sadness, but have compensated by their kindness to students. Very maternal.
Ivy Maggs — Formerly a part-time domestic servant for Jane Studdock; now driven out of the town by the N.I.C.E. and living at St. Anne's. Jane is puzzled at first by her status as an equal at the house. Ivy's husband, incidentally, is in prison for petty theft.
Merlinus Ambrosius — The wizard Merlin, awoken and returned to serve the Pendragon and save England. Receives the powers of the eldila. He has been in a deep sleep since the time of King Arthur, and both sides initially believe he will join the N.I.C.E. It is a shock when he appears at St Anne's.
Mr. MacPhee — A scientist, skeptic, and rationalist, and close friend of Dr. Ransom. Wants to fight the N.I.C.E. with human powers. An argumentative character who claims to have no opinions, merely stating facts and illustrating implications. The awoken Merlin believes MacPhee to be Ransom's "fool" (i.e. jester), because MacPhee is "obstructive and rather rude...yet never gets sat on". (The character may have been based on William T. Kirkpatrick, former headmaster of Lurgan College and an admired tutor of the young Lewis.)
Mr. Bultitude — Last of the seven bears of Logres, he escaped from a zoo and was tamed by Ransom, who has regained man's pre-fallen authority over the beasts. St. Anne's

Major themes
The novel's central theme — that pure materialism is incompatible with ethics and, ultimately, human life — is, as Lewis stated, based on his own treatise The Abolition of Man. An extreme example of this theme is his portrayal of the leaders of N.I.C.E., two of whom (Frost and Wither) have become nihilists with no recognizably human motives as a result of their quest for a purely objective mode of thought. Furthermore, Lewis portrays their materialism as having, perhaps inevitably, degenerated into a false front: a disgust with physical life and a fascination with the esoteric and occult have turned them in fact into avid gnostics. Genuine scientific materialism of the Victorian type is portrayed as comparatively innocent, and is represented by Ransom's "official sceptic" MacPhee and by the chemist Hingest, who breaks with the N.I.C.E. on discovering that it has "nothing to do with science".

Materialism and nihilism
The novel is Lewis's most overtly political fiction, illustrating how the alliances of state, industry, and academia and the manipulation of the mass media might move England towards fascism.
In the novel Merlin criticizes Mark and Jane for their use of contraceptives (it is not made clear whether Ransom, or Lewis, agrees). The novel cannot be said to attack feminism as the concept did not exist at the time the novel was written, but it defends the family and traditional marriage. Lewis attacks what he considered sexual perversion: Fairy Hardcastle, a prominent villain, is an implied lesbian and sadist (and veteran of Mosley's British Union of Fascists), who forces her attentions on non-consenting "fluffy" female captives.
Lewis portrays in a negative light the trend of relativistic non-traditional teaching of children, using one character's voice to observe that while "experimenting" on children would be met with outrage, for some reason sending them to "experimental schools" was considered progressive. He also attacks in passing the "Humanitarian Theory of Punishment" as an infringement of the human rights of the criminal: if punishment is intended to be therapeutic rather than retributory, there is no clear end point at which the offender has paid his debt to society.

Cecil Rhodes and imperialism
Like the dialogue between the Oyarsa and Professor Weston in Out of the Silent Planet, the discussion between Ransom and Merlin dramatizes Lewis's opinions on modern Western materialistic culture:
"The poison was brewed in these West lands but it has spat itself everywhere by now. However far you went you would find the machines, the crowded cities, the empty thrones, the false writings, the barren beds: men maddened with false promises and soured with true miseries, worshipping the iron works of their own hands, cut off from Earth their mother and from their Father in Heaven".
This criticism is clearly based on religious and conservative premises. Merlin later expresses horror at finding a world in which there is no longer an Emperor "whose office it is to put down tyrants and give life to dying kingdoms". Much of this criticism also chimes with contemporary attacks on globalism and capitalism from the modern Left.

Critique of global capitalism
St Anne's own domestic politics are egalitarian. There are no servants. Jane is somewhat taken aback, despite her theoretical egalitarian beliefs, that Ivy treats the educated and middle-class residents as equals. Also, men and women share alternate shifts for the housework. The idea behind this is that men and women tend to work differently, or as one female character says, you may get a man to do something, but it only causes trouble to try to get him to help.

Egalitarianism at St Anne's
The "Banquet at Belbury", where the N.I.C.E. leadership are made unable to comprehend each other's language and are thus undone, is clearly based on the Biblical story of the Tower of Babel, to which the book's name also refers. (Specifically, it is taken from a quotation from the sixteenth-century Scottish poet Sir David Lindsay, which also serves as the book's motto: "The shadow of that hyddeous strength [the Tower of Babel] sax myle and more it is of length".)
When describing to the reawakened Merlin the conditions in the modern world, Ransom says "it is as in the days when Nimrod built a tower to reach heaven". Though not specifically stated in the Bible, long-standing later tradition (attested in Jewish, Christian and Muslim sources alike) attributes to the hunter-king Nimrod the building of that tower, an ultimate act of rebellion against God's authority. The N.I.C.E. scientists do not build a physical tower, but they and their Satanic patrons, the "macrobes", are rebelling against God. This makes them Nimrod's successors, deserving of the same Divine retribution which fell upon Nimrod and his followers.

Nimrod and the Tower of Babel
Members of the N.I.C.E. "inmost circle" engage in a secret Satanic ritual of stripping naked and bowing down to the re-animated head of the criminal Alcasan, which actually houses one of the demonic macrobes. All the while they chant, "Ouroborindra! Ouroborindra! Ouroborindra ba-ba-hee!".
The name "Ouroborindra" is presumably composed of Ouroboros, the mythical worm or dragon swallowing its own tail, and the Hindu god Indra.
In the Christian interpretation Ouroboros is a symbol of the limited confines of the material world and the self-consuming transitory nature of a mere "worldly existence", and Chesterton, in The Everlasting Man, uses it as a symbol of the circular and self-defeating nature of pantheistic mysticism and of most modern philosophy. While Hindus in general reckon Indra as among the forces of Good, he is also considered the least perfect of their gods and the most inclined to sinful behavior, and on one occasion was punished for sexual misconduct by "a curse that one thousand phalluses would cover his body in a grotesque and vulgar display, and that his reign as king of the gods would meet with disaster and catastrophe".

The Satanic "Ouroborindra"
At the end, the group at St Anne's reflect for a time on the meaning of their quest. Dimble suggests that there is something peculiarly English about the way their land is poised between Logres and Britain. McPhee protests that this is just a complex way of saying there are good and bad people. Ransom says that it means more than this, and it is wrong to think the position especially English. Every country and culture has its own form of good and its own ideal — it is evil that is standardized and monotonous.
Whereas the N.I.C.E. represents death and nihilism, St Anne's represents life. Not only human beings, but animals and angels as well join in cosmic harmony at the end. Mark and Jane Studdock are about to be reunited, and the Oyarsa of Perelandra is about to take Ransom back to Venus. Under her influence all the animals are going out in pairs — Mr Bultitude, the bear, has found his Mrs Bultitude.

Satire on academic politics
Parts of That Hideous Strength are a homage to Lewis's close friend and colleague, J.R.R. Tolkien. A major theme of the novel is that as time goes on, the universe keeps coming to sharper and sharper points, and that while magical communion with nature may have been lawful in ancient times (in the time of Merlin and King Arthur), now such activities are unlawful and almost impossible. There are references to "Numinor" (an unintentional misspelling of Númenor, a word Lewis had heard while listening to Tolkien reading his stories aloud, but had never seen written down), which is the last land in Tolkien's mythology before the Undying Lands. Magic was apparently lawful and accessible in Númenor, to some extent, and there were non-human intelligences accessible to human beings. This sounds very much like the description of Tolkien's Middle-Earth, and twice in the chapter "They Have Pulled Down Deep Heavens on Their Heads" Lewis specifically references the Earth as "Middle-Earth": once in Dr. Dimble's discussion with his wife, and once when Merlin states that if the gods come down it will unmake all of Middle-Earth. However, here, the non-human intelligences are not elves or immortals such as Gandalf; they appear to be spirits.
This novel, unlike the previous two books, shows the influence of Charles Williams. Similarities to William's supernatural thrillers include the non-exotic setting, the gathering of an informal team of heroes rather than a single protagonist, the focus on a temporarily estranged married couple, and the use of Arthurian legend. Olaf Stapledon was an indirect influence. The description of the "Head" is similar to that of the Fourth Men in Last and First Men. In the book's preface, Lewis said of Stapledon: "…Mr Stapledon is so rich in invention that he can well afford to lend, and I admire his invention (though not his philosophy) so much that I should feel no shame to borrow".
The character of Jules is believed to be a caricature of H. G. Wells, whose ideas conflicted sharply with Lewis's. The popularity of Wells, whose views Lewis and his friends disagreed with, had been one of the negative influences inspiring the Space Trilogy, although it should be noted that in Out of the Silent Planet and elsewhere Lewis stated his debt to Wells in imaginative terms. (Lewis was throughout his life able to admire a very wide range of literature, even if he disagreed with it.) The historian A. J. P. Taylor, a fellow at the same Oxford college as Lewis, speculates in his memoirs about several other characters in the book being based on certain people at the University.