Master documentarian William Greaves presents extraordinary archival footage from a legendary 1972 gathering at Duke Ellington's Harlem townhouse. Convened by Greaves and Ellington, the gathering brings together towering cultural figures and architects of Black artistic life for an intimate exchange of memory, laughter, and reflection. Completed decades after it was first filmed, ONCE UPON A TIME IN HARLEM preserves an irreplaceable moment in Black cultural history.