The next in the Austin Family Series by Madeleine L'Engle is The Young Unicorns. The wiki has a pretty good plot summary.
Themes such as individuality, individuality within community, trust, love, the nature of redemption are explored in this book. It was a slow start, but once I got to page 100, I finished the book in an evening.
"Dave" Davidson is a former gang-banger. He's gotten out, and in trying to put his past behind him, he's denying its part in his life. He prefers to be a "lone wolf" and not allow others become important to him in any way. Then, he gets involved with the Austins and a mystery. The mystery forces him to rely on others, realize that he does love the Austin family, and come to terms with his past. He is forced to live life understanding the "challenge and hope." Without denying his past, he learns to look forward to his future ... in community. He learns he doesn't have to be alone to be himself.
The title doesn't totally make sense to me, my best guess is that unicorns are "unique" and, yet, it is the Young Unicorns. Uniqueness in community, perhaps?
Next up fiction-wise, will be Arm of the Starfish (which should have perhaps been read between The Moon by Night and The Young Unicorns, but it isn't that big of a deal) I would definitely recommend it before Ring of Endless Light, which has always been my favorite, and will follow Arm.