Tess Gerritsen joined the front ranks of thriller writers with her "New York Times" bestseller, "Harvest." Now she weaves utter medical authenticity into another novel of gripping suspense, as a dedicated woman doctor probes too deeply into the cause of a lethal, mystifying outbreak.

The overnight ER rotation at Springer Hospital suits Dr. Toby Harper just fine -- until its calm is shattered by a man Toby admits one quiet night. Delirious and in critical condition from a possible viral infection of the brain, he barely responds to treatment...and then he disappears without a trace. But before Toby can find her missing patient, a second case occurs, revealing a chilling twist: evidence of an infection that can only be spread through direct tissue exchange. Soon Toby's on a trail that winds from a pregnant sixteen-year-old prostitute to an unexpected tragedy in her own home. Only then does she discover the unthinkable: an evil, deadly design to the frightening epidemic.