Which C.S. Lewis novel was published in 1945 as the final book of the Space Trilogy?

That Hideous Strength was published in 1945 as the final book of C.S. Lewis’s Space Trilogy.

The novel follows Mark and Jane Studdock amid a conflict involving the sinister National Institute of Coordinated Experiments, or N.I.C.E. Although much of the action takes place in an English university and rural community, the story connects its social and scientific ambitions to the wider planetary conflict of the trilogy.

The first two books are Out of the Silent Planet, published in 1938, and Perelandra, published in 1943. Elwin Ransom links the three novels, though Ransom’s role and the settings differ significantly from book to book.

The title comes from a line by David Lindsay’s 1920 novel A Voyage to Arcturus. That Hideous Strength is sometimes labeled fantasy rather than science fiction, but it is commonly classified as the concluding volume of Lewis’s science-fiction trilogy.