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.

The story of a band of spotty, noisy, working-class kids with “no future,” who shook the boring, corrupt Establishment to its core, threatened to bring down the government and changed music and culture forever.