On a hot day in July 1919, five black youths went swimming in Lake Michigan, unintentionally floating close to the white beach. An angry white man began throwing stones at the boys, striking and killing one. Racial conflict on the beach erupted into days of urban violence that shook the city of Chicago to its foundations. This mesmerizing narrative draws on contemporary accounts as it traces the roots of the explosion that had been building for decades in race relations, politics, business, and clashes of culture.