Gigantic mutant locusts rampage over the countryside. Wainwright and Aimes begin to track down the source of the mysterious occurrences, and quickly discover that the locusts which ate the grain have grown to the size of a city bus. The monsters have eaten all the crops in the area, and now have turned to human beings as a source of sustenance. It is also clear that they are headed for Chicago. Wainwright and Aimes meet with General Hanson, Colonel Sturgeon, and Captain Barton to try to come up with a solution. Machine gun and artillery fire seem ineffective against the creatures, and there are far too many to effectively deal with all at once. The United States Army and Illinois National Guard are called upon to help protect the city. But the monsters quickly invade Chicago, and begin to feast on human flesh, as well as several buildings.