Reliquary by Douglas Preston and Lincoln Childs
Pendergast Book #2
Deep in the underground of New York City, a whole world of mole people exists. When bodies begin to surface, missing heads, authorities are reminded of the terrible museum beast of a year before. Pendergast, D'Agosta, and Margo Green are back on the case to discover who these "Wrinklers" are and how they can be stopped while also averting a biological disaster.