A judgement in stone

Eunice is taken on as a housekeeper by a family of four. She has kept her illiteracy a secret and is obsessed with continuing to keep it so. Unknown to her new employers, she has already murdered the father she had been caring for, and has falsified her references. Her inability to adapt to her place in society is masked by the cunning with which she conceals the truth about herself. Misinterpreting every act of kindness she is offered by her employers, she eventually turns on them, stealing the guns that are normally kept locked away. With the aid of a fellow social misfit, she murders the entire family. But Eunice's illiteracy prevents her from recognizing and disposing of a written clue that was left behind. Eventually a tape recording of the shooting made by one of the victims is discovered. Eunice is charged with the crime, and is mortified when her illiteracy is revealed to the world during the court proceedings.