A three-year-old boy dies, having apparently fallen while trying to reach a bag of sugar on a high shelf. His grandmother stands accused of second-degree murder. Psychologist Susan Nordin Vinocour agrees to evaluate the defendant, to determine whether the impoverished and mentally ill woman is competent to stand trial.

Vinocour soon finds herself pulled headlong into a series of difficult questions, beginning with: was the defendant legally insane on the night in question? As she wades deeper into the story, Vinocour traces the legal definition of insanity back nearly two hundred years, when our understanding of the human mind was in its infancy.

Competency and insanity, she explains, are creatures of legal definition, not psychiatric reality, and in criminal law, "insanity" has become a luxury of the rich and white. With passion, clarity, and heart, Vinocour examines the troubling intersection of mental health issues and the law.