A Judgement in Stone is Rendell's masterpiece (well, along with one or two others). It is popular opinion among her fans, and it is also true. I have never read a better book on the class division in England; any books that deal with probing the minds of the mad are written only by Rendell herself.
"Eunice Parchman killed the Coverdale family because she could not read or write", is its famous first line, and a brilliant one it is too. The crime writer Henning Mankell has said that it is his ambition to write a crime novel where, from the beginning, the reader knows exactly what is going to happen, but continues to read the rest of the book for a desperate need to find out more details such as why and how. In time, Mankell may well achieve that, but with A Judgement in Stone Rendell already has.
Despite that the reader knows what's going to happen, there is more compulsion to turn the pages even than in a normal detective story. The psychological insights and the gradual movements towards the foreshadowed events are absolutely gripping - this novel is possibly Rendell's most focused depiction of a mind driven to madness, mad actions, despite not being inherently "mad".
It's also told in a wonderful style. A retrospective one, looking back on events as if you are being told a story by a person in the room with you. It's almost delivered as a true-crime case study, a proper scientific rendering of murder.
It is truly superb. Only Rendell could write a novel where the psychoses of an illiterate lead to catastrophic murder. The writing is brilliant, the description of colliding classes is inspiring and very well-done indeed. Tension and suspension fill the pages until the very last, as the two women (Eunice and her friend Joan, follow down this terrible path.) How did it happen? What exactly set it off? Why? All questions the reader desperately wants to know. Also particularly chilling is the way that, throughout the book, the characters have so many opportunities to escape their fate, but they never take. There is always a possibility for escape, but we know they don't take it. Rendell snatches it away before long in any case.
An excellent book. It's only 200 pages, but it says so very much about people and society that it'd be easy to re-read it as soon as you finish it the first time.