Documentary which explores how Dolly Parton, Linda Ronstadt and Emmylou Harris's careers took off in the 1970s with very distinct takes on country before they ended up uniting as close harmony singers and eventually collaborated on 1987's four-million-selling debut album, Trio. This is the story of Dolly, Linda and Emmylou’s friendship and musical sisterhood over several decades, how they united their different audiences and raised the game for women in the country tradition.