A young NASA doctor must combat a lethal microbe that is multiplying in the deadliest of environments -- space -- in this acclaimed blockbuster of medical suspense from Tess Gerritsen, bestselling author of Harvest, Life Support, and Bloodstream. Gravity Dr. Emma Watson has been training for the adventure of a lifetime: to study living beings in space. But her mission aboard the International Space Station turns into a nightmare beyond imagining when a culture of single-celled organisms begins to regenerate out of control -- and infects the space station crew with agonizing and deadly results. Emma struggles to contain the outbreak while back on Earth her estranged husband, Jack McCallum, works frantically with NASA to bring her home. But there will be no rescue. The contagion now threatens Earth's population, and the astronauts are stranded in orbit, quarantined aboard the station -- where they are dying one by one...