The last few million humans live in the southern hemisphere -- mainly Australia. The northern hemisphere has been almost totally vaporized by nuclear war. What's left is cooking in a lethal dose of radiation, which is drifting inexorably south. We follow the lives of an American nuclear sub commander (his wife and children dead); his Australian girlfriend, Moira; an Australian naval officer with a young wife in denial and with a newborn baby; and a scientist who feels responsible. They live their familiar lives in whatever time is left, vainly hoping to find an escape.