When 20-year-old Odetta Holmes-classically trained as a vocalist and poised to become "the next Marian Anderson"-veered away from both opera and musical theater in favor of performing politically charged field hollers, prison songs, work songs, and folk tunes before mixed-race audiences in 1950s coffee houses, she was making one of the most portentous decisions in the history of both American music and Civil Rights. Released the same year as her famous...