When a local television station reports that something strange has landed in the small town of Abrose, Iowa, the government's covert Office of Scientific Intelligence (OSI) is called to investigate. Andrew Nivens, his son Sam and NASA scientist Mary Sefton are the team who make the frightening discovery: an alien parasite creature so insidious it attaches to the backs of human beings and sends piercing tendrils to the brains of its hosts, absorbing all their knowledge and memory--controlling their minds and feeding on the victim's consciousness. Against impossible odds Nivens, Sam and Mary must find a way to eliminate the aliens who seem unstoppable--without killing the innocent human hosts.