John Sayles is, in a way, the true successor to the great John Cassavetes, and this Deep South fable about the birth of rock ’n’ roll is one of the best of his 40-year career.

Set in 1950, it has Danny Glover as Tyrone, the veteran proprietor of the Honeydripper Lounge who, deep in debt, struggles to compete with the jukebox joint next door. Laying off his longtime blues singer (Mable John), for one night only he engages the famous Guitar Sam to try to turn things round.

Sam doesn’t turn up, so Sonny (Gary Clark Jr), a young drifter with a new-fangled electric guitar in his case, has to become the ace-in-the-hole. But first Tyrone has to blackmail the Sheriff (Stacy Keach), a racist who has arrested Sonny for vagrancy and rented him out as a cotton picker to the highest bidder.

Beautifully acted — especially by Glover and Charles S Dutton as Tyrone’s old friend — the writing makes you laugh with and fear for these hard-pressed black Americans in the Alabama of the Fifties.

Another plus point is the music, which Sayles maintains heralded the coming of rock ’n’ roll while upholding the tradition of the blues. This is the film-maker’s 16th film and it is not his most fluent technically, sometimes seeming like a piece of music theatre translated to the screen. But it comes from the heart.