An Army Colonel, under orders to vacate an underground Bio-Chem research bunker at the close of World War II, illegally buries toxic waste in an isolated Keyly, Kansas farmer's field. Forty-five years later, a brown odorous slime saturates the local farmer's storage bins filled to the brim with crops grown from a new experimental seed that has merged with the waste. Agriculturist Ronald Huntly retires from the Army and relocates to Keyly after attending his mother's funeral there. Upon arriving in Keyly, Huntly and the local residents soon learn the contaminated crops have caused hoards of grasshoppers to mutate into carnivorous killer swarms. The Governor asks the U.S. Army for help warding off the vicious attackers. But when the troops arrive, they are under orders to exterminate more than just insects.