The Light and the Dark is the fourth novel in C. P. Snow's Strangers and Brothers series.

Calvert was based on Snow's friend, Coptic scholar, Charles Allberry.

Set in England in the lead-up to and during World War II, it portrays Lewis Eliot's friendship with the gifted scholar and remarkable individual Roy Calvert, and Calvert's inner turmoil and quest for meaning in life.

"[4] The title also has resonance to the buildup to war, the sense of catastrophe so widespread in the 1930s, and Calvert's mental health problems.

and summarized; "Good writing and interesting characterizations fail to keep the book from tedious periods.