What is the title of the third novel in C.S. Lewis's Ransom Trilogy?

That Hideous Strength is the third novel in C.S. Lewis's Ransom Trilogy.

The novel was published in 1945 and follows the growing conflict between a secret scientific organization and forces resisting its attempt to remake society. Unlike the first two books, which focus strongly on interplanetary travel, That Hideous Strength is set mainly on Earth, particularly in an imagined English university town.

The trilogy's first novel is Out of the Silent Planet, published in 1938. It is followed by Perelandra, published in 1943. Together, the books follow the philologist Elwin Ransom and combine science fiction with mythology, theology, and moral philosophy.

That Hideous Strength has sometimes been read alongside Lewis's concerns about technocracy, propaganda, and the misuse of science. Its title echoes a line from David Lindsay's 1920 novel A Voyage to Arcturus, which Lewis admired.