Vanish - Tess Gerritsen (Rizzoli & Isles #5)

Goodreads 4.14 

A blessed event becomes a nightmare for pregnant homicide detective Jane Rizzoli when she finds herself on the wrong side of a hostage crisis in this timely and relentless thriller from the New York Times bestselling author of Body Double. 

A nameless, beautiful woman appears to be just another corpse in the morgue. An apparent suicide, she lies on a gurney, awaiting the dissecting scalpel of medical examiner Maura Isles. But when Maura 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, where 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. And only she can solve it if she survives the night. From the Hardcover edition.