Professor Millward has stayed with his books, when the country was abandoned more than twenty years ago,[4] and lost track of the others' attempts to colonize the rapidly transforming jungles and deserts of the south, also via the radio, some years later.[5] He is now sheltering from the cold in the edifice of a London university. Over months, he is haunted by a mysterious sound from the north, which he attributes to "mountains on the march",[6] in his dreams. Roaming about the snow-bound familiar roads and houses of the city long after the last stray dogs have disappeared from them, he is surprised by wolves, reindeer, and polar bears, and therefore ponders if the roaring in the north may be caused by an expedition from North America across the frozen-over Atlantic or by efforts to free the land from ice and snow with atomic bombs.