Uncovering one corner of American roots music that hasn't benefited from the recent folk revival, Sterlin Harjo's heartfelt doc "This May Be the Last Time" begins as a testament to Native American oral history in its most lyrical form, before suggesting its subject may be more universal than that. Filtering painstaking research on the evolution of Creek Nation hymns through a tragic narrative from Harjo's family history, the director's first nonfiction feature is artful and illuminating -- though, for all its implication of other cultures in its study, unavoidably specialized in appeal. Already acquired by the Sundance Channel, it'll be perfectly served by a TV premiere this spring.

An Oklahoma-based son of the Seminole tribe himself, Harjo begins by matter-of-factly relating the story of his grandfather's mysterious death in 1962 -- a sincere pretext for a probing examination of the singular-sounding spiritual music that nursed his family through their grief. Through interviews with sundry community members and outside academics, Harjo draws an improbably convincing genealogical line between these endangered Creek hymns and the traditions of Scottish traditional songs, African-American gospel and even the Rolling Stones. Tech contributions are humbly enhancing, particularly Royce Sharp's bell-clear sound design.

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