New York City. 1897. Sara Howard has opened a pioneering private detective agency. She reunites with formidable alienist Dr. Laszlo Kreizler and New York Times journalist John Moore to find the kidnapped infant daughter of a Spanish dignitary.

Sara uncovers a clue at the Siegel Cooper Department Store that leads her into dangerous territory. Moore struggles to balance his personal and professional life as he investigates a link to New York's criminal underworld.

Sara and Moore return to the killer's abandoned house in search of new information about their suspect. Kreizler faces ruin after a tragic incident at the Institute. Sara and the team are enlisted to rescue another missing child.

Sara, Kreizler and Moore travel to Brooklyn in search of clues. Byrnes plans to double-cross the team as the killer's behavior becomes unhinged. Sara and Moore's feelings for each other force them to confront difficult choices.

While Sara, Moore and Kreizler struggle with decisions about their future paths, New York is in the grips of an all-out manhunt for the killer, and the team must overcome the wrath of the police and an underworld gang on the rampage.