Margo Green is a graduate student in ethnopharmacology working at the New York Museum of Natural History. Grieving the recent death of her father, she struggles with pressure from her mother to abandon her studies and return home to help with the family business. Her academic focus involves classifying indigenous plants, a highly specialized skill that proves vital when she begins analyzing packing fibers from a doomed Amazonian expedition. She approaches the growing crisis with a methodical, scientific mindset despite her initial insecurities.

Special Agent Pendergast is a slender, impeccably dressed investigator from the FBI's New Orleans field office. He possesses a courtly Southern demeanor that masks a formidable intellect and a willingness to bypass bureaucratic hurdles. Tracking a series of ritualistic killings, he brings his unconventional methods to the New York Museum of Natural History. He operates outside standard procedures, relying on obscure knowledge and sharp observational skills to find connections that local authorities miss.

Dr. Frock is the chairman of the evolutionary biology department and a distinguished physical anthropologist. Confined to a wheelchair following childhood bouts with polio and malaria, he commands respect through his intellect. He champions the controversial "Callisto Effect" theory, which argues that evolution occasionally produces sudden superpredators due to environmental pressures. He views the museum murders through a clinical lens, eager to find empirical proof for his marginalized academic ideas.

Lieutenant Vincent D’Agosta is a pragmatic, world-weary officer with the New York Police Department. Tasked with managing the initial crime scenes within the museum, he struggles with the sprawling, unmapped architecture and uncooperative staff. He brings a grounded, procedural approach to law enforcement that contrasts with the FBI's eccentricity. He prioritizes the safety of civilians and his officers above the museum's public relations concerns.

William Smithback, Jr. is a cynical, rumpled journalist commissioned to write a promotional book about the Superstition exhibition. He constantly seeks sensational details to elevate his writing, putting him at odds with the museum's strict public relations guidelines. He navigates the institution's internal politics to uncover hidden shipping records and forgotten historical files. His self-serving ambitions gradually align with Margo's search for the truth.

Winston Wright is the director of the New York Museum of Natural History. He operates as a pompous administrator entirely focused on funding, attendance, and institutional optics. He consistently downplays the severity of the violence occurring within his building to protect the upcoming Superstition exhibition. He utilizes his political connections to override safety protocols and suppress police investigations.

Ian Cuthbert is the museum's deputy director and a calculating enforcer of the institution's policies. He handles the logistical oversight of the Superstition exhibition and aggressively pushes for its opening despite the escalating danger. He harbors a deep disdain for Dr. Frock's unconventional theories and actively restricts access to the museum's historical archives.

Lavinia Rickman serves as the chief of public relations for the museum. She acts as a strict institutional censor, demanding that all external communications present the museum in a flawless light. She actively alters records, hides historical journals, and threatens legal action to maintain her carefully constructed narratives. Her dedication to the museum's prestige directly enables the ongoing threat.

The Mbwun Creature is a massive, quadrupedal predator haunting the dark subbasements and air ducts of the museum. Described in Kothoga legends as a supernatural beast, it leaves behind three-pronged claw marks and a foul, goatish odor. The beast targets the human hypothalamus, possessing immense strength and speed. It relies heavily on a keen sense of smell to navigate its nocturnal hunts.

Gregory Kawakita is an ambitious assistant curator in the evolutionary biology department. He developed a highly advanced genetic sequence extrapolator program that can predict biological traits from raw DNA. Driven by a desire for tenure and academic recognition, he considers switching his allegiance away from the controversial Dr. Frock. He prioritizes his own career advancement over collaborative scientific efforts.

George Moriarty is the earnest young assistant curator responsible for mounting the Superstition exhibition. He is a dedicated academic who genuinely believes in the educational value of the artifacts on display. While he adheres strictly to administrative rules, his inherent helpfulness leads him to assist Margo in tracking down poorly documented shamanistic plants.

Ippolito is the museum's director of security. He places absolute faith in a newly installed, computerized security grid consisting of heavy steel doors and motion sensors. He relies on technological solutions to secure the sprawling building, often dismissing the need for manual patrols or conventional police tactics.

Special Agent Spencer Coffey is an arrogant investigator from the FBI's New York field office. Brought in through political maneuvering by the governor's office, he attempts to usurp Pendergast's authority over the case. He prioritizes high-profile security theater over practical safety measures, implementing an untested computer lockdown system for the exhibition gala.

John Whittlesey is a museum anthropologist who led an ill-fated expedition into the Amazon Basin in 1987. Driven by a desire to prove the existence of the Kothoga tribe and restore his academic reputation, he pushed deep into the jungle despite the desertion of his team. His discoveries set the current events at the museum in motion.

Officer Beauregard is a uniformed policeman assigned to guard the museum's sealed hallways. Distracted by thoughts of an upcoming fishing trip, he grows increasingly frustrated by strange noises behind the exhibition doors and the lack of support from his dispatcher.

Dr. Jörgensen is a retired botanist who possesses crucial historical knowledge about the 1987 Amazon expedition. Originally slated to join Whittlesey's team, he provides Margo and Smithback with vital context regarding the Kothoga tribe and the legends surrounding the artifacts.