After World War III, Australia is the only remaining haven for mankind. However, wind currents carrying lingering radiation all but condemn those on the continent to the same fate suffered by the rest of the world. When the survivors receive a strange signal from San Diego, Cmdr. Dwight Towers (Gregory Peck) must undertake a mission with Lt. Peter Holmes (Anthony Perkins) to see if there is hope for humanity -- leaving behind Moira (Ava Gardner) and Mary (Donna Anderson), the women they love.