It is the spring of 1948. In the still cool evenings of Pittsburgh's Hill district, familiar sounds fill the air. A rooster crows. Screen doors slam. The laughter of friends gathered for a backyard card game rises just above the wail of a mother who has lost her son. And there's the sound of the blues, played and sung by young men and women with little more than a guitar in their hands and a dream in their hearts. August Wilson's Seven Guitars is...