Officer Beauregard finishes his notebook entry and decides to file his report later. Thinking of his planned fishing trip to the Catskills, he looks forward to the end of his shift in 10 minutes. He hears a muffled pattering from behind the sealed exhibition doors but finds nothing. However, when the sound comes a third time, he radios the dispatcher, who mocks him and refuses to send backup. Beauregard loses his temper and demands they send McNitt. The dispatcher reluctantly complies—but he sends the man on a route that passes through the exhibition. A sudden commotion from inside the exhibition leads Beauregard to unlock the doors and go in with his weapon drawn.

Minutes later, McNitt radios in from the rear entrance, reporting that Beauregard is nowhere to be found and is not responding to his radio. When Beauregard’s relief arrives, neither McNitt nor the dispatcher reports him for abandoning his post.

D’Agosta and Pendergast are driven through Manhattan by an incompetent driver provided by the New York FBI office. To pass the time in traffic, Pendergast shares his new findings. Lab analysis of the claw fragment found both gecko and human DNA. The autopsy on Jolley shows that the thalamoid region of the brain was removed, and tests for saliva on the brains of both Jolley and the first boy victim came back positive. The blood on a painting was Jolley’s, and the three-pronged scratches on the vault door are consistent with the victims’ wounds.

At a laboratory, scientists Buchholtz and Turow explain that their tests on the claw were positive for human DNA and gecko DNA, with most genes in the sample unidentified. By elimination, the scientists conclude that the DNA probably came from a human but was degraded or contaminated; alternatively, the claw may be from a lizard and heavily contaminated with blood from its human victim. Pendergast requests further tests to determine the function of the gecko genes, then tells them to send the bill to the FBI’s director of special operations—which D’Agosta recognizes as payback for the bad driver.

On Thursday morning, multiple disturbances erupt at the museum. A man claiming to be the pharaoh Toth causes a disturbance in the antiquities wing. An hour later, a woman runs screaming from the Hall of Great Apes after seeing something in a bathroom, captured on film by a television crew. Around lunchtime, a group pickets the Superstition exhibition. That afternoon, a philanthropist offers a $500,000 reward for the capture of the Museum Beast.

Undisclosed to the press, four employees quit without notice, 35 take unscheduled vacations, and nearly 300 call in sick. By curfew, police have responded to four unverified sightings, and the museum switchboard has logged over 100 creature-related calls, including bomb threats and offers of assistance.

Smithback finds Gregory Kawakita and asks him to help Margo with the genetic sequence extrapolator program, mentioning that her father died two weeks ago and that she may leave the museum. Kawakita is surprised but suspicious of Smithback’s altruism.

Smithback admits that he wants Kawakita to query the accession database for information on the Whittlesey expedition, believing that this expedition is linked to the murders. Kawakita retrieves a memo from Lavinia Rickman, in which she forbids all staff from speaking to the media or assisting anyone preparing books about the museum. Kawakita says that with his upcoming tenure review, he cannot help. He invites Smithback to go fishing on Sunday, and Smithback agrees.

D’Agosta responds to an emergency sighting in the computer room, where the shift supervisor reports a loud thumping from the electrical systems room. D’Agosta and two officers investigate but find nothing unusual. They post a guard there for the next 36 hours.

As D’Agosta prepares to leave, a heat alarm sounds: The mainframe is overheating. He concludes that the thumping came from failing air-conditioning compressors. Over an hour later, the room is chilly and appears normal. The posted officer notices a blinking error message on a terminal but ignores it.

Smithback sets up in a library carrel, frustrated that neither Moriarty nor Kawakita will help him access the accession database. His searches of microfilm and museum internal records turn up nothing new on the Whittlesey expedition. He coaxes a reference librarian into giving him the key to the library archives, then searches shipping receipts until he locates the bill of lading for the Whittlesey crates. The records indicate the ship’s name, the Strella de Venezuela, and its long layover in New Orleans.

At the microfilm catalog, he pulls up the October 1988 reel of the New Orleans Times-Picayune and finds a headline about the ship, learning why the crates were delayed in New Orleans for so long.

Unable to reach Frock, Margo invites Moriarty to her office to look at the accession database. Smithback arrives uninvited, and after Moriarty’s brief hesitation, Margo convinces him to proceed. The file for the Whittlesey expedition shows that all seven crates were moved to a secure vault on March 20, 1995, per Ian Cuthbert. The journal is listed as “temporarily removed,” and its detailed record has been erased with a high-security identification. Offended by Smithback’s speculations, Moriarty leaves.

Smithback shows Margo a newspaper article from October 1988 describing the slaughter of the crew of the Strella de Venezuela, with wounds matching those of the museum victims. The Whittlesey crates were on that ship; he believes that the ritualized murders have followed the crates from the Amazon.

Frock calls and agrees to meet Margo at one o’clock. Moriarty returns to apologize to Margo, then realizes that there might be a way to recover the deleted journal record. He warns Margo that his online explorations could be traced to her terminal, but she accepts the risk. The recovered record is partially corrupted but shows that Lavinia Rickman removed the journal on March 15, 1995, with Cuthbert’s approval and no return date. Margo realizes Cuthbert had lied about the journal being lost. When Moriarty implies that her grief over her father’s death is clouding her judgment, she leaves abruptly for her meeting with Frock.

Margo meets Frock and tells him about the Mbwun figurine’s three-clawed forelimbs. Frock theorizes that Cuthbert’s missing seed pods may have been reptilian eggs that hatched, though Margo points out this does not explain the murders on the freighter years earlier.

Pendergast arrives, and Frock reports that no artifact in the collection matches the agent’s theory of a claw weapon. Pendergast summarizes the case, stating that they must find a preternaturally strong killer that removes and likely eats the hypothalamus, hides in the subbasement, and has already killed two search dogs. He confirms the claw’s DNA showed both human chromosomes and gecko genes.

Frock presents his theory of the Callisto Effect, asserting that evolution periodically produces superpredators that cause mass extinctions. He argues the killer is a modern superpredator that arose to prey on the exploding human population and came back in Whittlesey’s crate. Pendergast remains politely unconvinced, still believing that the killer is human. On his way out, he deliberately leaves behind the DNA report, which Frock recognizes as a covert sign of cooperation.

Frock calls Cuthbert, demanding access to the Superstition exhibition and the Whittlesey crates; Cuthbert angrily refuses both. Frock decides to use an unsigned request form to force access, then realizes that he is physically unable to enter the space. Margo volunteers to go in his stead. Frock warns her of the professional risk but agrees. Giving her the unsigned form, the vault combination, and a key, he instructs her to look for eggs or cult objects in Whittlesey’s crate, stating that these will help to prove his theory.

Margo and Smithback meet at a stairwell landing and review their plan. Smithback will distract the guard while Margo slips into the secure area. Inside, Margo finds the correct vault and searches the smaller crate, finding a variety of items. The larger crate has been torn apart with ragged marks. At the bottom she finds a brittle, water-damaged envelope and shoves it into her bag along with a plant press, stone disc, and rattle.

She slips out, rejoining Smithback, and they evade the approaching Ian Cuthbert, who angrily questions the guard about intruders. Once safely away, Smithback and Margo open the pilfered envelope, which is addressed to H. C. Montague. Inside is a letter from John Whittlesey, dated September 17, 1987, from the Upper Xingu. Whittlesey writes that he is sending a man named Carlos back with the last crate while he goes on alone to search for Crocker. He notes that the enclosed figurine has reptilian attributes and hints of walking upright. He then asserts that the Kothoga and Mbwun legend are real and says his field notes are in his notebook.