I usually synopsize myself, but I don’t feel I’d do this justice. Goodreads does an excellent job:
The First World War laid waste to a continent and permanently altered the political and religious landscape of the West. For a generation of men and women, it brought the end of innocence - and the end of faith. Yet for J.R.R. Tolkien and C.S. Lewis, the Great war deepened their spiritual quest. Both men served as soldiers on the Western Front, survived the trenches, and used the experience of that conflict to ignite their Christian imagination. Had there been no Great War, there would have been no Hobbit, no Lord of the Rings, no Narnia, and perhaps no conversion to Christianity by C.S. Lewis.
Unlike a generation of young writers who lost faith in the God of the Bible, Tolkien and Lewis produced epic stories infused with themes of guilt and grace, sorrow and consolation, Giving an unabashedly Christian vision of hope in a world tortured by doubt and disillusionment, the two writers created works that changed the course of literature and shaped the faith of millions. This is the first book to explore their work in light of the spiritual crisis sparked by the conflict.