Over the years, Edward Fowler, an American academic, became a familiar presence in San'ya, a run-down neighborhood in northeastern Tokyo. The city's largest day-labor market, notorious for its population of casual laborers, drunks, gamblers, and vagrants, has been home for more than half a century to anywhere from five to fifteen thousand men who cluster in the mornings at a crossroads called Namidabashi (Bridge of Tears) in hopes of getting work...