In July 1988, a smuggler named Ven works the Belém docks at night, increasingly convinced that the foreman suspects his operation. Working with Ricon, the assistant harbormaster, Ven diverts cargo boxes from upriver shipments and hides them behind museum crates marked for New York until they can be loaded onto US-bound freighters.

After the foreman leaves his office, Ven uses a copied key to enter the warehouse and navigates toward a stack of crates labeled MNH, NEW YORK, which arrived from Porto de Mos the previous fall. He has been using the space behind them to stash his goods and plans to leave before the crates are shipped.

As Ven approaches, he smells a strange, “goatish” odor of decay. Ignoring his instinct to flee, he squeezes into the cramped space behind the crates. Something slams him against the wall with tremendous force, and before he can scream, he feels a final, sharp pain in his skull.

On a Sunday at the New York Museum of Natural History, two young brothers wander through darkened halls searching for dinosaurs, separated from their parents. Billy, the older boy, finds a metal door behind a canvas barricade leading to a spiral staircase descending into darkness. He tells his brother to wait while he explores. When Billy doesn’t return, the younger boy follows—slipping through the barricade and descending into the dark, where a strange smell fills the air and his calls go unanswered.

On Monday morning, graduate student Margo Green arrives at the museum to find police cars and ambulances in the staff courtyard. She and her colleague, Assistant Curator Gregory Kawakita of the Evolutionary Biology Department, discover that the corridor to Margo’s basement office is blocked by police tape; guards are preventing staff from entering the sealed area. In the staff lounge, Margo notices conservation expert Charlie Prine being escorted out by officers, his shoes soaked in blood.

Lieutenant D’Agosta of the NYPD enters the crowded lounge and announces that bodies have been found under suspicious circumstances. He closes the Museum and orders everyone to remain while officers sweep the building for a possible killer still inside. After D’Agosta leaves them under guard, Margo cannot stop thinking about the blood on Prine’s shoes.

An hour later, staff are released but must avoid taped-off areas. Journalist Bill Smithback, who is writing a book about the museum, tells Margo that Charlie Prine discovered the bodies of two young boys in the basement. Police are investigating the possibility of a wild animal attack and have brought in special coroner Dr. Matilda Ziewicz. Museum Director Winston Wright will hold a press conference to address the rumors.

In a harried press conference, Wright denies the press’s insinuations that the museum keeps wild animals. He repeatedly refuses to comment on the nature of the killings until autopsies are complete and insists that the upcoming Superstition exhibition will open as scheduled. The chaotic event ends with Wright visibly furious.

Margo visits her dissertation advisor, Dr. Frock, a distinguished physical anthropologist who now uses a wheelchair following childhood polio and malaria. His controversial “Callisto Effect” theory proposes that evolution sometimes produces short-lived aberrant species through sudden environmental pressures rather than gradual change. A fossil footprint of an unknown creature sits on his desk; as the only physical evidence for Frock’s theory, the object is often derided by critics.

Margo presents her research on Kiribitu plant classification, which Frock approves. He then raises the topic of the murders, expressing unease about the unusual force used on the bodies. He encourages Margo not to abandon her research despite her father’s recent death, and as she departs, he warns her to be careful.

Over lunch, Smithback tells Margo that police are using a bloodhound to track something through the museum’s vast spaces, including five miles of forced-air ducts and a warren of largely unmapped subbasement tunnels beneath the original building. He also mentions the persistent staff rumor of a “Museum Beast” that supposedly killed someone years ago.

George Moriarty, the young curator of the Superstition exhibition, joins their table. Smithback shows him edits made by Lavinia Rickman, the chief of public relations, who has been heavily censoring the manuscript for his commissioned book about the museum. Moriarty, whom Smithback despises for adhering to official guidelines, sides with Rickman, and Smithback makes an excuse to leave. Moriarty expresses interest in Margo’s ethnopharmacology work and asks to discuss the exhibition with her.

Professional tracker Jonathan Hamm waits in a basement corridor with his two hounds, Lieutenant D’Agosta, and two armed deputies. The dogs struggle to find a clear scent due to the contaminated crime scene and the chemical smell of preserved specimens nearby. D’Agosta admits that his blueprints do not cover the subbasement they are about to enter.

The team descends into dark, brick-lined tunnels. At a junction, one hound catches a strong air scent, and both dogs begin baying frantically. The first hound, Castor, breaks free and races into the darkness; the second, Pollux, follows. Their barking abruptly stops, replaced by a terrible shriek. A shape hurtles from the darkness, panicking the deputies, who fire twice, only to realize that they have just killed the fleeing Pollux. Further down the tunnel, the team finds Castor torn nearly in half. Amid Hamm’s dismayed silence at the carnage, D’Agosta calls off the search and leaves the scene for forensics.

Moriarty, who has been tasked with working on the upcoming Superstition exhibition, asks Margo to help identify some poorly documented shamanistic plants from the Cameroons for the display. They head to the sixth-floor storage vaults, where Moriarty unlocks a small vault crammed with Central African artifacts. When he estimates that the work will take 10 to 15 hours, Margo’s enthusiasm dims, but she reluctantly agrees to help despite her dissertation deadline.

Moriarty defends the exhibition against charges of sensationalism before inadvertently quoting his boss, Dr. Cuthbert, who called Frock “mentally unsound” and dismissed the man’s Callisto Effect theory. Offended, Margo walks away. A horrified Moriarty realizes that Frock is her advisor and quickly apologizes, explaining the long-standing feud between Frock and Cuthbert. Margo accepts his apology on the condition that he guide her out of the storage maze.

As they leave, Moriarty tells her about Kothoga tribe material in the exhibition, including a figurine of the mythical beast Mbwun, which will be a centerpiece. He confides that there has been high-level controversy surrounding the artifacts, as well as rumors of a curse. He adds that the Kothoga tribe materials are still in their original crates, which are now in the museum’s secure area. The crates were recently moved because they had apparently been tampered with, but Moriarty refuses to elaborate further on this point.

At 2:15 pm, Lieutenant D’Agosta waits in the Medical Examiner’s autopsy suite. Dr. Matilda Ziewicz arrives and begins the autopsy of William Bridgeman, one of the murdered boys. The body has massive head trauma and an enormous laceration across the chest. The entire back portion of the skull has been punched through, and some brain tissue is missing entirely.

Ziewicz identifies the missing brain regions as the thalamus and hypothalamus. Dr. Gross notes what appears to be a bite mark on the tissue, and Ziewicz observes three parallel lacerations consistent with sharpened fingernails or claws. Deep within the torso wound, Ziewicz extracts a claw, causing D’Agosta to exclaim in shock. Ziewicz dryly notes that his unprofessional outburst is being recorded.