When police find two skeletons locked in a bony embrace deep in the mud off the Manhattan shoreline, Natural History Museum curator Margo Green is called in to aid in the investigation. She soon realizes that the expertise the cops want is the result of her ordeal last year, battling the horrific beast loose in the basement corridors of the Museum. Because the skeletons show signs, not only of foul play, but of abnormalities point to thing: the awakening of a slumbering nightmare. Aided by Lieutenant D'Agosta, the enigmatic FBI agent Pendergast, and the brilliant scientist Dr. Frock, the search for answers will take Margo and her team far beneath the city of Manhattan, into an underworld few know exist - and fewer still would dare to go.