Midway through Martin Luther King, Jr's historic speech at the 1963 March on Washington, a voice rang out from behind him: "Tell them about the dream, Martin!" That voice belonged to Mahalia Jackson, King's close friend and one of the most revered gospel singers of the 20th century - Glorious Mahalia, a visionary tribute to Jackson's life by the internationally renowned Kronos Quartet, uses that moment as a springboard to explore the depth of Jackson's musical craft and its impact on the Civil Rights Movement, including her relationship with Clarence Jones and Studs Terkel, other luminaries of the time