I love Madelaine L'Engle's books, and this is one of her very best. It brings in many familiar characters, which was enjoyable, but in a very adult book about the pain and joy of real life.
Katherine Forrester Vigneras, a top concert pianist, appeared as a teenager in The Small Rain, here she is an old woman. Her life looked full of hope at the end of that book. However the war came, her jewish pianist husband suffered because Nazis broke his hands, she later fell in love with a Nazi and had a son that her husband treated as his own, but then he died aged only 7 in an accident on a funfair ride. These and other sorrows together with the joys of her life all give her a sensitivity that enables her to support the people she meets who tell her their troubles. In the end everything is connected.
As a young adult I found it a very profound book and it taught me that we grow and learn and change through compromise and suffering in ways that make us better and wiser people. It is, beyond everything, a book about forgiveness and hope, an uplifting book. It made a very deep impact on me and I have read it several times.