Single father Dan Logan lives with his teenage son Chris in Wyoming. While camping, a U.S. Army helicopter sprays the father and son with an experimental chemical that is being tested for use in biological warfare. The poisoning puts Chris into a coma, and when Dan seeks medical help, an army doctor

One evening for fun, Wyoming sheep rancher Dan Logan and his twelve-year-old son Chris camp out on their grazing land, pitching a tent and building a fire. Early the next morning, Dan's dog awakens him in the tent and anxiously leads him to Chris, who spent the night sleeping under the stars. Dan soon realizes that Chris, whose nose is bloody, is unconscious and extremely ill. As Dan scoops up Chris and carries him to his pickup truck, he notices many of his sheep lying dead on the ground. While racing to the nearest hospital, Dan, a widower, stops briefly at his neighbor Bill Parker's house and asks him to alert the local veterinarian about his dead sheep. At the hospital, a young Army doctor, Major Holliford, questions Dan about Chris's symptoms and suggests that Chris may be suffering from insecticide poisoning. Dr. Roy Cardwell, the Logans' longtime family physician, then arrives at the hospital, but tells Dan that Holliford, a specialist, is better equipped to treat Chris than he is. After Holliford places Chris in an isolation ward, Roy urges Dan to be admitted to the hospital and examined by Holliford as a precautionary measure. Meanwhile, at nearby Fort Howard, Colonel Alan A. Nickerson, a group of Army officers and researchers, and Dr. Spencer, the local public health official, meet to discuss the previous night's "accident." Nickerson's aide, Major Jack Reintz, explains that just before dawn, Fort Howard helicopter pilots were testing MX3, a new chemical agent, when the nozzle on one of their sprayers got stuck and inadvertently dumped the agent in and around the Logan property. Dr. Tom Janeway, an Army researcher working at Chevington Laboratories, where MX3 is manufactured, reveals that Chris and Dan will likely die from their MX3 exposure. Janeway argues that, no matter what happens, the two should be monitored as test cases, and Nickerson orders that details of the accident be kept from the public. Although Chris's condition worsens, Holliford and Roy assure Dan, who has not been allowed to see his son, that Chris will recover. Chris dies soon after, but Holliford, afraid of losing Dan as a test subject, instructs Roy and the hospital staff not to reveal anything to him. That night Chris's death is reported on the local news, and even though it is attributed to accidental pesticide poisoning, Spencer becomes concerned that the real story will soon come out. At the hospital, meanwhile, Dan repeatedly asks to see Chris, unaware that his son's body is being autopsied in the hospital morgue. Concerned about Dan's growing agitation, Holliford orders him sedated. The next day, Roy sneaks a look at Dan's hospital records and, disturbed, confronts Holliford about his situation. Holliford admits that Dan has only a few days to live but insists he not be told so that the Army can continue testing him. Outraged by Holliford's callousness, Roy defies the command and announces he is revealing the truth to Dan. Holliford immediately arranges for Dan to be moved, but as he is being wheeled down the hospital corridor, Dan notices an orderly carrying Chris's clothes in a plastic bag and becomes suspicious. That night, Spencer tries to mollify Dan, promising him he can visit Chris in the morning, but as soon as Spencer leaves, Dan dresses and slips out of his room. Eluding detection, Dan sneaks down to the morgue and there discovers his son's body. Quietly crying and cursing, Dan flees the hospital and after a night spent walking, steals a motorcycle. While riding, Dan sees a string of Army vehicles heading toward his home and realizes he cannot return to his ranch. Armed with a newly purchased rifle, Dan instead goes to Spencer's house and, at gunpoint, demands to know what killed Chris. Spencer resists telling Dan, until Dan is startled by Spencer's cat and sprays it with bullets. Unnerved by Dan's actions, Spencer reveals all. Now filled with a vengeful hate, Dan buys some explosives and constructs several crude bombs. That night, Dan, who is growing increasingly ill from the MX3, plants his bombs at the Chevington Laboratories, cold-bloodedly killing a guard and two policemen before causing the entire facility to explode in a fiery ball. Fleeing the scene, Dan then forces a truck driver to take him to Fort Howard and shoots the M.P. guarding the entrance. After allowing the driver to escape, Dan speeds the truck toward the fort's administration building. Dan is soon surrounded by Army vehicles and, though dizzy and weak, tries to shoot his way out. Overhead, an officer in a helicopter orders Dan to surrender, but Dan collapses and, after going into violent convulsions on the ground, dies. The next day, as Dan's body is about to be shipped off to Denver for further study, Roy drives up and laments his friend's fate and his part in the cover-up.