Smithback and Margo visit Dr. Jörgensen, a retired botanist. When he sees Whittlesey’s letter, Jörgensen is visibly shaken. After Margo explains their belief that the Whittlesey expedition is linked to the murders, he agrees to talk.

Jörgensen explains that he was originally to join the expedition as botanist but was excluded when Maxwell became co-leader. Whittlesey’s secret goal was to find the Kothoga on a restricted tepui, while Maxwell became sidetracked by a discovery of mysterious seed pods. The party split; Maxwell returned while Whittlesey pressed on, never to be seen again. Maxwell’s group died in a plane crash, and all expedition documentation burned with them. The tepui was later destroyed by napalm and mining, which is why the museum never sent a follow-up expedition. When the crates finally arrived, a young anthropology candidate named Montague was assigned to curate them. He soon vanished, abandoning his apartment and all possessions.

Jörgensen then shares a Kothoga legend: The tribe made a pact with a devil named Zilashkee, sacrificing their own children to receive his child as a servant. The beast, called Mbwun, could not be killed, only controlled; however, it turned on them. In the aftermath of the expedition’s disasters, Jörgensen had wondered if the Kothoga had finally managed to rid themselves of Mbwun.

In his office near closing time, George Moriarty sits alone, frustrated by his social awkwardness with Margo. To lift his spirits, he searches the museum’s accession database for forgotten artifacts and discovers a collection of unresearched Sumerian clay tablets that could enhance the exhibition. He leaves, intending to retrieve the tablets from storage just before the curfew.

At the temporary command post, D’Agosta finds a stranger rifling through Pendergast’s desk. The man identifies himself as Special Agent Spencer Coffey and produces official orders from Washington, backed by memos from the governor and a US senator, transferring authority from Pendergast to the FBI’s New York Field Office. When Pendergast arrives, he calmly insists the opening must be postponed, but Coffey dismisses his concerns and declares that the opening will proceed with enhanced security. Pendergast plans to file his objections but does not otherwise protest.

After Coffey leaves, D’Agosta expresses frustration that Pendergast is yielding. Pendergast explains that with the governor formally requesting FBI intervention, the transfer was inevitable. However, Coffey cannot remove him entirely, and now Pendergast is free to pursue his own approach. He asks D’Agosta to continue assisting him, and D’Agosta agrees.

In Rickman’s office, Smithback receives a memo imposing strict new conditions on his work. All interviews must occur in Rickman’s presence, she will take notes instead of him, and he is forbidden from discussing museum matters without her written permission. He threatens to sell the murder story to a commercial publisher, but Rickman warns that the museum’s law firm would destroy his career with a breach of contract lawsuit. Seeing something in her desk drawer, Smithback appears to capitulate and agrees to sign.

While Rickman steps out, Smithback extracts Whittlesey’s journal from Rickman’s desk drawer and steals it before signing the memo. In Margo’s lab, he reads it aloud. The key entry describes the expedition repacking a crate after a specimen jar broke, then encountering a ruined hut where an old woman emerged and warned them about Mbwun—the son of the devil Zilashkee—saying the curse would destroy anyone who took it. The final entry notes that Crocker is missing and that Whittlesey is sending Carlos back while pressing on alone. Smithback is disappointed, believing the journal contains nothing new.

Pendergast and D’Agosta tour the museum’s security system with Security Director Ippolito. The building is divided into five cells that can be sealed by steel doors; they are designed to trap thieves when motion-sensitive artifact chips are triggered. For the party, cell two will be sealed, with four guarded doors left open. Pendergast questions whether the system’s schematics accurately reflect the older basement areas.

Coffey arrives and orders three of the four open doors sealed, leaving only one entrance and exit. Pendergast strongly objects, warning that guests will be trapped in the event of an emergency. He also argues that the complex, untested computer system should be disabled in favor of conventional armed guards and foot patrols. Coffey mocks the suggestions and dismisses Pendergast. D’Agosta confronts Coffey, calling him a disgrace, and Coffey announces that D’Agosta will be pulled from the case after the party.

In the auxiliary botanical lab, Kawakita demonstrates his genetic sequence extrapolator for Margo, explaining it can predict the traits of evolutionary links between species from DNA. He mentions that early tests vindicated Frock’s Callisto Effect theory, though Kawakita feels underrecognized and is considering switching advisers. After he leaves, Margo begins sequencing DNA from various plant specimens for her dissertation.

While waiting for results, Margo realizes that in Whittlesey’s journal, the old woman warned about Mbwun before Whittlesey entered the hut—meaning that she was referring to something in the open crate, not the figurine that the scientists later found in the hut itself. Reviewing the crate’s contents, Margo examines plant specimens taken from near the hut, then sequences the crate’s packing fibers on impulse. She discovers that Kawakita’s program cannot even identify the kingdom of the organism, as it has detected both plant and animal genes. Margo identifies the unknown genes as proteins and hormones from the vertebrate and human hypothalamus. Realizing the implications, she picks up the phone.

Pendergast returns to the museum with old blueprints and studies them for an hour. He then loads a Colt .45 Anaconda, pockets extra ammunition, and moves through the museum—now bustling with party preparations—into the non-public back corridors. At four o’clock, with all agents at Coffey’s briefing, he unlocks the Superstition exhibition entrance, emerges minutes later, and descends into the museum’s basements.

At Margo’s lab, she walks Frock through her discoveries. She states that the old woman’s warning referred to the crate’s contents, not the figurine, then reviews her findings about the packing fibers’ mixture of plant and animal genes. When she mentions that the DNA includes numerous hypothalamic hormones, Frock deduces that the plant is infected with a reovirus forcing it to produce these hormones; he concludes that the creature has been feeding on the hormone-saturated fibers. When the crates were moved to the secure area 10 days ago, cutting off its supply, it turned to killing humans for the same hormones, which can be found in the brain’s thalamic region. However, it requires roughly 50 human brains to match the hormone concentration in half an ounce of the plant.

Margo theorizes the Kothoga cultivated the plant and that Mbwun is the plant’s name, not the creature’s. She also connects the New Orleans freighter murders to the creature following the crates, explaining Pendergast’s involvement. Frock laments that the destruction of the tepui ecosystem drove the creature to follow the crates to New York. Realizing they can use the extrapolator to analyze DNA from a claw fragment Pendergast had provided, they load the data. The program estimates 55 minutes to completion. The time is 5:15 pm.

As dusk falls and a thunderstorm approaches, the museum closes to the public and workers prepare for the party, which is set to begin at seven o’clock. D’Agosta positions his men throughout the Hall of the Heavens, noting he hasn’t seen Pendergast since the confrontation with Coffey. The massive steel security doors begin descending, sealing the perimeter.

Coffey approaches and demands that D’Agosta assign two officers to guard an exterior door. D’Agosta refuses, arguing that his personnel are needed inside to protect guests, while Coffey has deployed most of his FBI agents outside. Coffey dismisses him and walks away.

Kawakita’s program completes its analysis of the claw DNA, describing a large, quadrupedal creature with a robust build, a mix of primate and reptile genes. It is extremely strong and fast, with the potential for human-level intelligence. Frock notes that the creature is nocturnal, with an extraordinary sense of smell but poor eyesight. Because the olfactory sense is more primitive, its reactions to smell will be highly instinctual. He grows alarmed, realizing that the concentrated hormonal scent of thousands of party guests will be an irresistible lure. They deduce that because three days have passed since the last killing, the creature is now desperate to kill. Frock declares they must stop the exhibition gala immediately.