Which 1933 book is C.S. Lewis’s autobiographical account of his conversion?

The Pilgrim’s Regress is C.S. Lewis’s 1933 autobiographical account of his conversion.

The Pilgrim’s Regress: An Allegorical Apology for Christianity, Reason and Romanticism was Lewis’s first published work after his conversion to Christianity. Published in 1933, it uses an allegorical journey to present ideas and experiences connected with his movement from atheism toward Christian belief.

Lewis later described his intellectual and spiritual development more directly in Surprised by Joy, published in 1955. That later book is often mistaken for the conversion account requested here because it is explicitly autobiographical. The Pilgrim’s Regress instead combines autobiographical elements with the structure of John Bunyan’s The Pilgrim’s Progress and includes characters representing competing philosophies and attitudes.