In the mid-1920s, young children began to vanish from neighborhoods around New York City. It took the police a decade to find their abductor, an unassuming 64-year-old handyman named Albert Fish. Fish had committed crimes of unspeakable horror: He had not only abducted and murdered the children, but also tortured and, in some cases, eaten them. During Fish’s trial, some of the country’s most prominent psychiatrists debated the exact nature of Fish’s crimes. Was he evil or insane? Who had the power to determine where one ended and the other began? At stake was not just the prospect of justice for Fish and his victims, but also the future of the new science of criminal behavior—the idea that society’s worst monsters needed to be both punished and understood. Award-winning journalist Deborah Blum tells the story of a notorious cannibal killer, the detective who brought him to justice, and the scientists who tried to make sense of his crimes.