Which C.S. Lewis novel features the character Mark Studdock and the organization NICE?

That Hideous Strength features Mark Studdock and the organization NICE.

Published in 1945, That Hideous Strength is the third book of Lewis's Space Trilogy. It follows Mark Studdock, a sociologist drawn into the National Institute of Co-ordinated Experiments, usually abbreviated as NICE. The organization presents itself as a force for scientific and social progress, but its ambitions involve manipulation, centralized power, and the attempted transformation of humanity.

Unlike the trilogy's first two novels, which travel to Mars and Venus, this book is set primarily in an English university town and nearby countryside. Its title echoes a line from David Lindsay's 1920 novel A Voyage to Arcturus. Readers sometimes remember the book chiefly as science fiction, but it also functions as a satirical and philosophical warning about technocracy, propaganda, and the loss of human moral limits.