This will likely make more sense to readers from US & Mexico than elsewhere; it's at least partially about their countries' relations, particularly as they relate to immigration.
A future US that is no longer a big power, with parts of the country in anarchy & outside of national administration. A Mexican charity is providing medical help to some of these anarchies. Story is of such a medical help trip of a man named Zipakna, a representative of charity, to one of these anarchies - a trip that later turns into a horrific adventure.
Fact sheet.First published: Asimov's, February 2008.