Alan Lomax spent decades recording the Mississippi Delta, and this film gathers his footage of the musicians, preachers, and laborers who shaped the blues. It opens with the 1933 trip he made as an eighteen-year-old alongside his father John Avery Lomax, hauling recording equipment into the American South for the Library of Congress, and follows the work forward through later expeditions into levee camps, prison farms, and rural churches. Lomax interviews sharecroppers and songsters on their own porches and in the fields where they worked, letting them explain what a given song was for, whether it kept time on a chain gang or carried a funeral. Fife-and-drum bands, work songs tied to the rhythm of an axe, and unaccompanied field hollers appear alongside the familiar guitar blues, making the case that the music grew directly out of forced labor and segregation rather than existing apart from it. Lomax himself narrates, treating the musicians as the authorities on their own tradition.