He hopes to prove that they still do exist and in the process learn more about their culture, including their lizard god Mbwun ("He Who Walks On All Fours"), supposedly the son of Satan.

NYPD Lieutenant Vincent D'Agosta leads the investigation into the museum basement, while museum leadership, including curator Winston Wright, deputy head Ian Cuthbert, and public relations director Lavinia Rickman, attempt to keep the murders under wraps in the lead-up to the grand gala opening of the new "Superstition" exhibition featuring wealthy benefactors.

When a security guard suffers a similarly brutal death, FBI Special Agent Aloysius Pendergast arrives to aid in the investigation, while the search spreads to the tunnels under the museum.

They deduce that the creature is a predator of formidable strength, speed, and intelligence, and is dependent on the now-extinct plant fibers for nutrition; in its absence, it has been slaughtering humans and consuming their hypothalamus as a substitute.

At the same time, an NYPD officer panics and opens fire on the security control room, destroying the central switching box and shutting down the museum's power.

D'Agosta leads Smithback and a group of gala attendees down into the tunnels to seek an escape route, and the creature attacks, killing several people.

The group from the gala reaches the sewers through rising stormwater and find the creature's lair, an underground chamber filled with corpses and trinkets.

Four weeks later, the survivors convene, and Pendergast explains that the Kothoga created the Mbwun by feeding a human the strange plant that Whittlesey had discovered and shipped back to the museum, which results in the subject transforming into the creature.

The museum directors covered up evidence of Montague's disappearance and moved the crates into the heavily fortified vault; unable to access them, the Mbwun turned to murdering people and animals in the sewers and underground tunnels for their hypothalamus.