Like A Circle of Quiet, the book is autobiographical and takes place at "Crosswicks," the L'Engle/Franklin home in Connecticut. As the title indicates, L'Engle's mother, freshly a great-grandmother, is living with them, and her health and cognitive ability is swiftly declining. Throughout the book--really, like A Circle of Quiet, a collection of journal entries--the author deals with losing the mother that she used to know to senility and incontinence, as well as the effects and ramifications of death.
I've never had anyone close to me die, so I can't relate to this book as much as I could to A Circle of Quiet or Walking on Water, but it's superbly written (L'Engle's words always seem to be alive and breathing), and I imagine that it would be a great comfort to those who are dealing with death.
As with "A Circle of Quiet" there are little gems along the way -- L'engle is a gifted writer, and reading her thoughts is a privledge. Overall, though, I found her style dispassionate and erudite, not what I would have expected from a personal memoir.