One day the people of New York City awake two find a couple of 2000-foot-tall figures standing in the harbor. The story describes the various ways that people cope with this event over the course of the next twelve months. I think that what Doctorow was going for is the idea that death looms over all of us, and is its own type of monstrosity, even though most of us going about our daily lives are unaware of the impending doom. Or something like that, anyway.