In cars, trains, buses and tube, the one topic of conversation was the black sky and mysterious disappearance of dust.

It was remarkable, too, how incredibly well washed and neat everybody looked, from the grimiest labourer to the proprietress of a beauty salon. Dust was on the march, from skins, clothes, streets, buildings -- everywhere. Even the slums, rotten with the accumulated dirt of years, were bright and resplendent, something for the train travelers to gaze upon in stunned wonder.

This removal of dust seemed to be a boon to mankind -- but it turned out to be a deadly scourge, and unless it was stopped millions of people would die!