Corporal Russell Gary works as an Army recruiter in a small Illinois town. He is a veteran of combat duty in Vietnam in the 1969 revision; in the original work, he is on leave from service in the Korean War. He awakes from an overnight binge to learn that the city has been almost destroyed by a sudden, mysterious bombing attack. Gradually, over the next few months, after wandering through one deserted, ravaged area after another, Gary concludes that a nuclear attack, accompanied by a deadly plague, has decimated the entire area east of the Mississippi River, extending from the delta northward to Lake Winnibigoshi in Minnesota.
Government troops along the Mississippi River guard against plague-ridden intruders trying to escape into the relatively intact western half of the country. Gary and a few others he meets along the way—including a teacher, a farmer, scavenging packs of plunderers, and a teenage girl with whom he has a brief affair—have survived apparently because they are immune to the disease.
Empowered by his combat training and by his wits— in Vietnam he was not only a decorated soldier but an “experienced and unscrupulous black-marketeer”—and undeterred by the probability that he is a carrier of the plague, Gary determines to cross the Mississippi and rejoin his military unit. Finally, after years of waiting, suffering, and disillusionment with the government that apparently has deserted him and his fellow survivors, Gary hijacks a jeep bound for the border and bluffs his way across.
When suspicious soldiers detain him, he escapes into the safe zones. It is only a matter of time before he realizes that he is indeed infecting others with the deadly plague. In an ironic epilogue, Gary flees pursuing troops and crosses the border back into the plague zone. Now reduced to virtual starvation, he makes his way to a cabin, where he is almost killed by a woman, one whom he had met and befriended years before. He subdues her and determines that together they will continue the battle for survival.