A psychologist, a newspaper illustrator, a secretary and a police commissioner begin an investigation outside the law to find a serial killer targeting boy prostitutes in 1896 New York City.
The investigation heats up as Sara gets her hands on a clue and Kreizler tries to connect the evidence left behind by the serial killer; tensions rise within the police department.
Innovative evidence leads the team to discover a crucial element in the case has gone missing; Kreizler and Moore interview a witness to find out what happened to Moore at the brothel; Sara attempts to live in a world outside the investigation.
Kreizler and Sara discuss the capacity to kill; Moore goes on a date; Byrnes and Capt. Connor keep an eye on a potential suspect; Roosevelt finds himself under public scrutiny.
The team learns more about the killer; Moore and Sara share an intimate moment; Kreizler seeks advice from an old mentor; Roosevelt takes action.
The team hatches a plan to catch the killer; Moore checks in on a friend; Kreizler faces his own self-doubt about the investigation; Roosevelt attends an event with the city's elite; Sara looks into Kreizler's past; Connor acts on impulse.
Kreizler and Moore follow a lead; Sara visits a hospital and is forced to confront her past; Cyrus, Kreizler's carriage driver, recovers from his injuries; Byrnes and Connor plot against the team; Detectives Marcus and Lucius Isaacson work on a clue.
Kreizler and Moore travel to Washington, D.C.; Sara goes rogue in pursuit of the truth; Lucius tells Marcus a secret; Byrnes and Connor tighten their grip on the investigation.
Kreizler mourns the loss of a friend; Sara pushes the team to forge ahead; Moore warns his friend the killer will strike again; Cyrus seeks revenge.
Kreizler confronts the demons of his past; Moore tells Sara the truth; Connor takes matters into his own hands; the team closes in on the killer as time runs out.