"A judgement in stone" is the story of a crime, and the reasons behind it. All that happens is in direct relation to a secret, Eunice Parchman's secret.
Eunice, the housekeeper of the Coverdale family, seems to be merely a dull woman with an insipid personality. She is cold and quite solemn, but not violent, at least she doesn't seem to be. However, events would prove otherwise, as the reader is informed from the very first page of "A judgement in stone": "Eunice Parchman killed the Coverdale family because she could not read or write".
This is the story of how an apparently normal person is ridden by the all-powering obsession of protecting a secret she deems shameful, that she is illiterate. How far will she go to avoid the disclosure of that fact is something you will learn if you read this book, although you already have a pretty important clue...
On the whole, I can say that I highly recommend this book. The main character isn't likeable ("A stone that breathed was Eunice, as she had always been"), but the story is engaging and well-written. Moreover, the writer managed to write a convincing psychological study of Eunice that allows the reader to look into the mind of a cold-blooded killer. Those are the main reasons why you won't be able to stop reading this book once you start it :)