Which C.S. Lewis novel, published in 1945, is the final volume of his Ransom Trilogy?

That Hideous Strength is the final volume of C.S. Lewis’s Ransom Trilogy, also known as the Space Trilogy. It was published in 1945 and follows the earlier novels Out of the Silent Planet and Perelandra.

The story shifts much of its action to Earth, where Mark and Jane Studdock become involved with the sinister National Institute of Coordinated Experiments. The novel combines science fiction, mythic elements, social criticism, and Christian themes, while continuing the presence of the philologist Elwin Ransom.

The title comes from a line by David Lindsay in A Voyage to Arcturus, quoted as “the hideous strength” of modern technological power. The trilogy’s books were not published in strict chronological order of their fictional universe, but That Hideous Strength is unambiguously the third and final published novel.