The United States government is given a warning by the pre-eminent biophysicists in the country: current sterilization procedures applied to returning space probes may be inadequate to guarantee uncontaminated re-entry to the atmosphere.Two years later, seventeen satellites are sent into the outerfringes of space to "collect organisms and dust for study." One of them falls to earth, landing in a desolate area of Arizona.Twelve miles from the landing site, in the town of Piedmont,a shocking discovery is made: the streets are littered with the dead bodies of the town's inhabitants, as if they dropped dead in their tracks.