Vanish : a novel / Tess Gerritsen.

A blessed event becomes a nightmare for pregnant homicide detective Jane Rizzoli when she finds herself on the wrong side of a hostage crisis. A nameless, beautiful woman appears to be just another corpse in the morgue. But when Boston medical examiner Maura Isles unzips the body bag and looks down at the body, she gets the fright of her life. The corpse opens its eyes. Very much alive, the woman is rushed to the hospital. But the bizarre soon turns lethal. With shockingly cool precision, she murders a security guard and seizes hostages, one of them a pregnant patient, Jane Rizzoli. Who is this violent, desperate soul, and what does she want? As the tense hours tick by, Maura joins forces with Jane's husband, FBI agent Gabriel Dean, to track down the mysterious killer's identity. When federal agents suddenly appear on the scene, Maura and Gabriel realize that they are dealing with a case that goes far deeper than just an ordinary hostage crisis. Only Jane, trapped with the armed madwoman, holds the key to the mystery, if she survives.