That Hideous Strength is the third novel in what is known as C.S. Lewis's "Space Trilogy" (the first two being Out of the Silent Planet and Perelandra, respectively). These works of science fiction are notably out of keeping with the rest of Lewis's writing; most of his works are either children's fantasy (The Chronicles of Narnia) or theological nonfiction (The Problem of Pain, The Abolition of Man, etc.). Lewis's prodigious talent, however, lends itself to this genre as well; his science fiction, while less focused on the science aspect than most novels of the genre (perhaps it could be better described as "space fantasy"), is of very high quality.
Originally published in 1945, before The Chronicles of Narnia, That Hideous Strength (with the subtitle A Modern Fairy-Tale for Grown-ups) differs from the previous two novels in that neither of the main characters in the story is the philologist Professor Elwin Ransom, although he is still a central figure in the plot. Instead of traveling to another planet, as Ransom did in Out of the Silent Planet (Mars) and Perelandra (Venus), the action takes place entirely on earth. It is an almost dystopian novel about a modern scientific institution (the N.I.C.E.) that proves to be less innocuous than it might present itself to be. Certain elements of the plot bear a remarkable resemblance to Madeleine L'Engle's A Wrinkle in Time, and Lewis himself wrote that the idea behind that novel is very similar to that of his essay collection The Abolition of Man).
This trilogy is some of Lewis's only fiction intended for adults (in the company of Till We Have Faces and The Pilgrim's Regress, arguably along with The Great Divorce). Interestingly, the concept for the trilogy emerged in a discussion with Lewis's friend J.R.R. Tolkien; the conversation concluded with an agreement for Lewis to write a "space travel" story and Tolkien a "time travel" one. Tolkien never completed The Lost Road, but Lewis's space trilogy came to fruition. Interestingly, the character of Elwin Ransom is at least partially based on Tolkien himself, by his own admission in his letters.
