The narrator and Dr. Kreizler’s assistant in the investigation, Moore is a police reporter who learns about the practical applications of Kreizler’s psychological theories.

Appointed as the liaison to Kreizler’s investigation, Sara is a pioneering young woman aspiring to be a police detective, contributing significantly to understanding the killer’s profile.

The real-life New York City police commissioner who authorizes the clandestine investigation, embodying themes of reform and courageous action against police corruption.

A detective with modern investigative techniques, Lucius is one of the Isaacson brothers who adds forensic expertise to the investigation team.

The taller Isaacson brother who, like Lucius, brings crucial forensic skills to Kreizler’s team, aiding significantly in the novel's murder investigation.

The serial killer whose grim actions propel the narrative, eventually revealed to have a traumatic past that factors into Kreizler’s psychological profiling.

Kreizler’s trusted maid, whose past experiences typify the exploitation of vulnerable individuals within the story’s context.

Kreizler’s servant and bodyguard, whose backstory of childhood trauma underscores key thematic elements of suffering and exploitation.

A young servant in Kreizler’s household, whose street-smart skills assist in advancing the investigation.

A former tenacious detective implicated in representing police corruption and brutality within the novel.

A prominent gangster whose complex character reveals a thoughtful and strategic alignment with Kreizler’s investigation.