What was C.S. Lewis’s first published book of prose fiction?

The Pilgrim’s Regress was C.S. Lewis’s first published book of prose fiction.

Published in 1933, The Pilgrim’s Regress is an allegorical novel subtitled An Allegorical Apology for Christianity, Reason and Romanticism. Its central character, John, travels through a landscape shaped by ideas, temptations, and competing philosophies. The title deliberately recalls John Bunyan’s influential Christian allegory The Pilgrim’s Progress.

Lewis wrote the book after returning to Christian belief, and it reflects his attempt to explain the intellectual and emotional path that led him to faith. Unlike the later Narnia books, it is aimed primarily at adult readers and uses dense symbolic material.

The novel is sometimes mistaken for Lewis’s first published work of any kind. His first published book was Spirits in Bondage, a 1919 poetry collection issued under the name Clive Hamilton.