An alien spacecraft sets down in rural Iowa, and top-secret government agents Andrew Nivens (Donald Sutherland) and his son, Sam (Eric Thal), are sent to investigate. Coming along is NASA biologist Mary Sefton (Julie Warner), and together they make a startling discovery: alien parasites capable of taking over the minds of human beings. And the creatures are multiplying. The race is on for the team to stop the invaders before they turn all of humanity into zombie slaves.