Plot
In south Texas, an unknown force invades and neutralizes a top-security United States Air Force ICBM command bunker. An Air Force unit, led by Major Baker, investigates and finds an unauthorized scientist at the secured base, Dr. Bradford Crane, who was tracking a swarm of killer bees when they attacked the bunker. General Slater orders two helicopters to check the area, whereupon they are destroyed by the swarm. Crane insists to Slater that the base was attacked by the same African killer bees that destroyed the helicopters. Helena Anderson, one of the base's doctors, supports Crane's story.
In the nearby countryside, the swarm attacks the Durant family. The mother and father die from the bee stings, but their son Paul escapes in their car. Despite being stung, Paul makes it into town, crashing into Marysville town square, where the citizens prepare for the annual flower festival. The boy is brought before military personnel, where due to the aftereffects of the bee sting, he hallucinates a vision of giant bees attacking him.
Dr. Walter Krim confirms to Crane that the war against the bees they have feared for a long time has started. At the gates of the base, Slater confronts county engineer Jud Hawkins, who demands to see the corpse of his son, an airman in the bunker whom the bees killed. Hawkins takes the body bag and departs. Slater suggests airdropping poison on the swarm, but Crane considers the ecological possibilities of the situation, as the poison will wipe out plant growth for a decade or more.
Recovering from his earlier bee attack, Paul and his friends search for the hive to firebomb it and avenge his family. This only angers the bees, who invade Marysville and kill hundreds. Crane and Helena take shelter at the local diner with pregnant café waitress Rita Bard. Reporter Anne McGregor watches from the safety of her news van, hoping to get exciting footage about the siege. After this attack, and fear of another one, Slater suggests evacuating many of the townsfolk in a train. However, the bees attack the train, causing it to derail over a cliff and kill almost everyone aboard, including a love triangle made up of schoolteacher Maureen Scheuster, retiree Felix Austin and town mayor and drug store owner Clarence Tuttle.
Rita tries to board the ill-fated train but is saved at the last minute by going into labor and being confined to the hospital. She gives birth to her child while falling in love with the doctor in the process. Paul suffers a relapse from the effects of being stung earlier and eventually dies, devastating Helena and sending her into a rage about why the children have to die.
The swarm heads for Houston, Texas, and Crane decides to drop eco-friendly poison pellets on them, hoping the bees' senses will be harmed and they will stay away from the city. The plan, however, fails. Dr. Krim self-injects an experimental bee venom antidote, planning to track the results, but the trial proves fatal and he dies. Meanwhile, nuclear power plant manager Dr. Andrews is convinced that his plant can withstand the bees' attacks, ignoring the warnings of Dr. Hubbard. The bees nevertheless penetrate the plant, causing a nuclear explosion that annihilates Andrews, Hubbard, the plant and a nearby town.
Meanwhile, in Houston, Slater orders the city to be burned in the final hopes of defeating the swarm. Crane analyzes tapes from the bee invasion and concludes that a test of an alarm system at the ICBM bunker attracted the swarm into the base. The bees attack Houston, resulting in the deaths of Major Baker and Dr. Newman, one of Crane's associates. Slater sacrifices himself to save Crane and Helena from the bees. Helicopters playing the alarm sound from the ICBM bunker over loudspeakers lure the bees out to sea, where they douse the water with oil and set the swarm ablaze. Helena wonders if their victory was just temporary. Crane responds that he does not know, but decides that "if we use our time wisely, the world just might survive".
