When Catherine Lelievre (Jacqueline Bisset) hires mousy and taciturn Sophie (Sandrine Bonnaire) as a housemaid, she thinks that she found a treasure. Mr. Lelievre (Jean-Pierre Cassel) seems to agree with her, pointing out that the maid just has yet to learn how to serve dinner correctly.
Wealthy liberals, they treat her generously enough and expect diligence and reliability in return. However, Sophie didn't tell her new employers that she is dyslexic, and very soon she has terrible troubles with even such supposedly ordinary things as shopping lists.
She befriends outspoken postal clerk Jeanne (Isabelle Huppert), who occasionally helps her with the above-mentioned lists and tells her all sorts of gossip about the Lelievre family.
Mr. Lelievre, who suspects that Jeanne opens their mail, tells Sophie that Jeanne was charged with the murder of her four-year-old daughter and though she was later acquitted, he can't believe in her innocence. Thus he forbids Sophie to invite Jeanne to the Lelievre house, and the tension between Sophie and her employers increases.
What could have been a thriller in the hands of a different director, in the case of Claude Chabrol has become another witty and observant social commentary about the eternal confrontation between the rich and the poor. Ruth Rendell's novel A Judgement in Stone was previously filmed in 1986 in Canada.