After several strange balls of light invade the night sky over the small mountain town of Fulton, Montana, a series of missing person reports follow. As Kenneth Marshall, a lieutenant with the Montana State patrol, begins investigation into the matter, the US Army and several government agencies arrive and demand that he ceases all inquiries.
Upon meeting a well-informed professor from Missoula, Ken discovers that aliens have been involved with the disappearances of visitors from state parks for years and are currently responsible for the abductions in Fulton. Determined to destroy the aliens, Ken ends up hiding from the government, the army, and the aliens. Teaming up with two of his friends, and the professor, they begin searching for a way to destroy the creatures, who are using humans for food.