故事发生在1896年的纽约，那时的纽约一片繁荣景象，一边是科技的长足进步，一边是贫富差距的加剧。这时发生了一连串男童妓被残忍杀害的事件，新任警察局长（日后的第26任美国总统）西奥多·罗斯福找来了犯罪心理学家拉兹洛·克莱斯勒、记者约翰·摩尔去秘密调查。他们并非孤军奋战，时任局长秘书（日后成为首位女警探）莎拉·霍华德组织了一个行动小组，利用心理学和新兴的法医学，抽丝剥茧，去抓捕这个连环杀手。The Alienist opens when a series of haunting, gruesome murders of boy prostitutes grips New York City. Newly appointed police commissioner Theodore Roosevelt (Geraghty) calls upon criminal psychologist (aka alienist) Dr. Laszlo Kreizler (Brühl) and newspaper illustrator John Moore (Evans) to conduct the investigation in secret. They are joined by Sara Howard (Fanning), a headstrong secretary determined to become the city's first female police detective. Using the emerging disciplines of psychology and early forensic investigation techniques, this band of social outsiders set out to find and apprehend one of New York City's first serial killers.