In 1897 New York, a city of stark contrasts between opulent mansions and squalid tenements, former police commissioner Theodore Roosevelt tasks Dr. Laszlo Kreizler, a pioneering psychologist, with a new case. The daughter of the Spanish consul has vanished, and whispers point to a kidnapping ring that preys on the children of wealthy immigrants. Kreizler reluctantly reassembles his former team: John Moore, a society illustrator haunted by the brutality of their previous investigation, and Sara Howard, who has left the New York Police Department to open the city’s first private detective agency for women. Their search quickly uncovers a more sinister pattern. Several infants from poor families have also disappeared, their bodies never found, and the trail leads to a charismatic midwife named Libby Hatch. Posing as a caregiver, Hatch has infiltrated maternity homes and charitable hospitals, gaining access to vulnerable mothers and their newborns. As Sara navigates a male-dominated legal system and John battles his own demons, Kreizler becomes convinced that Hatch is not merely a kidnapper but a remorseless killer who disposes of children she deems unfit. The investigation forces Sara to confront the limits of her authority when a young mother is framed for infanticide, while John’s growing obsession with the case strains his engagement to a wealthy socialite. Meanwhile, a rival detective hired by the Spanish consul works at cross purposes, and corrupt city officials protect Hatch in exchange for her services in covering up inconvenient births. The narrative arc culminates in a desperate pursuit through the city’s newly constructed subway tunnels, where the team must prove Hatch’s guilt without the evidence being dismissed by a court unwilling to believe a woman capable of such evil. The resolution sees Sara embracing a harder-edged form of justice, Kreizler questioning his own methods, and John finding a measure of peace by documenting the forgotten victims, leaving the door open for the darkness to resurface in another guise.