One otherwise peaceful summer morning, New Yorkers strolling in Central Park come to a halt in unison, then begin killing themselves by any means at hand. At a high-rise construction site a few blocks over, it's raining bodies as workers step off girders into space. And all the while, the city is so quiet you can hear the gentle breeze in the trees. That breeze carries a neurotoxin, and what or who put it there (terrorists?) is a question raised periodically as the film unfolds. But the question that really matters is how and whether anybody in the Middle Atlantic states is going to stay alive. Focal characters are a Philadelphia high-school science teacher, his wife and math-teacher colleague, and the latter's little girl. Instinct says get out of the cities and move west; most of the film takes place in the delicately picturesque Pennsylvania countryside, with menace hovering somewhere in the haze.