In the year 1964, nuclear war has wiped out all life in Earth's northern hemisphere. After discovering San Francisco to be devastated and deserted, US submarine commander Dwight Towers (Gregory Peck) and his crew head for Australia, where they each cope with the situation in their own individual ways while awaiting the fall-out that will kill them: scientist Julian Osborn (Fred Astaire) achieves his life's ambition of winning an auto race; while naval officer Peter Holmes (Anthony Perkins) considers taking his life; and Towers finds romance with good-time girl Moira Davidson (Ava Gardner), who is determined to take one last chance at love.