Hidden deep beneath Manhattan lies a warren of tunnels, sewers, and galleries, mostly forgotten by those who walk the streets above.When the police find two skeletons in a bony embrace on the Manhattan shoreline, they call upon Natural History Museum curator Margo Green. They do not merely require her anthropological expertise, but her experience of a related investigation: a set of horrific murders last year at the museum.Margo must once again team up with FBI agent Pendergast, as well as the brilliant Dr. Frock, to try and solve the puzzle. The trail soon leads deep underground, where they will face the awakening of a slumbering nightmare.