I've read quite a few biographies of both J.R.R. Tolkien and C.S. Lewis, so I was worried this book would be too much of stuff I already knew, but it wasn't. It did a good job balancing its focus on Lewis, Tolkien, and Charles Williams, and Owen Barfield and even throwing in stuff about the other lesser-known members of the Inklings. The book did multi-page analyses of the the Inkling's most important works - decently insightful, too. There were some fresh ideas about books I've read and re-read and read about quite a lot.
The Fellowship: The Literary Lives of the Inklings