Which 1945 C.S. Lewis novel completed his Space Trilogy?

That Hideous Strength completed C.S. Lewis’s Space Trilogy in 1945. Unlike the first two novels, much of its action takes place on Earth, where a scientific institution pursues an ambitious and morally dangerous plan.

The novel follows Mark and Jane Studdock as they become entangled with the National Institute of Coordinated Experiments, usually called N.I.C.E. Its story combines social criticism, Arthurian elements, speculative science, and Christian themes. The title echoes a line from David Lindsay’s 1920 novel A Voyage to Arcturus.

The first two trilogy books are Out of the Silent Planet, published in 1938, and Perelandra, published in 1943. The series is therefore not a conventional sequence of planetary adventures. That Hideous Strength shifts the setting and style while continuing the trilogy’s concern with humanity, technology, power, and spiritual corruption.