In the future year of 1964, World War III has devastated the
Northern Hemisphere, killing all humans there. The
cobalt bomb's fallout is elevated compared to that of
atomic bombs and
hydrogen bombs. Air currents are slowly carrying the fallout to the
Southern Hemisphere, where
Melbourne,
Australia will be the last major city on Earth to perish. The American
nuclear submarine USS
Sawfish, commanded by Capt. Dwight Towers, arrives in Melbourne and is placed under
Royal Australian Navy command. Peter Holmes, a young Australian naval officer with a wife Mary and infant child, is assigned to be Towers' liaison. Holmes invites Towers to his home for a party and meets Julian Osborn, a depressive nuclear scientist who helped build the bombs. Towers develops a tentative attraction with Moira Davidson, a lonely alcoholic. Although Davidson falls in love with Towers, he finds himself unable to return her feelings because he cannot bring himself to admit that his wife and children in the United States are dead. A new scientific hypothesis suggests that radiation levels in the Northern Hemisphere might have fallen faster than anticipated, suggesting that radiation may disperse before reaching the Southern Hemisphere, or at least leave
Antarctica habitable. Soon after, the Australians also detect an incomprehensible continuous
Morse code signal coming from region of
San Diego, where there should be nobody alive to send it. Towers is ordered to command the
Sawfish, with Peter and Julian, on an investigation mission. Arriving at
Point Barrow, Alaska, the sub crew discovers that the radiation levels are not only highly lethal but higher than in the mid-
Pacific Ocean, meaning the dispersal hypothesis is wrong; there will be no salvation from the radiation. Stopping next in
San Francisco,
Sawfish finds the city devoid of life. A crew member with family in the city deserts and swims ashore, so he can die at home. The submarine next stops at a refinery near
San Diego, which has been pinpointed as the source of the mysterious Morse signals. A crew member discovers that the power source is still running on automatic control. Nearby, a
telegraph key has become entangled in a window shade's pull cord and a half-full bottle, and is being randomly pulled by an ocean breeze, causing the radio signals.
Sawfish returns to
Australia to await the inevitable. Towers is reunited with Davidson at her father's farm. He learns that all U.S. Navy personnel in
Brisbane are dead and that he has been given command of all remaining American forces. Osborn, having bought the fastest
Ferrari in
Australia, wins the
Australian Grand Prix, in which many racers, with nothing left to lose, die in fiery crashes. Fulfilling Towers' wish, Davidson has leveraged her connections to open the trout season early. Towers and Davidson go fishing in the country. As drunken revelers sing "
Waltzing Matilda" in the hotel bar, Towers and Davidson make love in their room. Returning to
Melbourne, Towers learns that the first of his crew members has
radiation sickness. With little time left, Towers takes a vote among his crew, who decide that they want to return to the United States to die. Osborn shuts himself in a garage with his Ferrari and starts the engine in order to end his life by
carbon monoxide poisoning. Others queue to receive government-issued
suicide pills at hospitals or clinics. Religious faith is important to Mary, who asks God to forgive them for choosing suicide. Before they swallow their pills, Peter and Mary reminisce about the day when they met on the beach. Towers says farewell to Davidson at the docks. Choosing duty over love, he takes the
Sawfish back to sea. Heartbroken, Davidson watches from a cliff as the
Sawfish submerges. Within a few days, the streets of
Melbourne are empty and silent. A
Salvation Army street banner over the bowed head of a war memorial figure reads: "There is still time .. Brother". ==Cast==