Meredith Wilson's hit 1957 Broadway musical was transferred to the screen in larger-than-life fashion in 1962. Robert Preston repeats his legendary stage performance as fast-talking con man Harold Hill, who goes from town to town selling citizens on starting a boy's band, then extracts money from them by ordering instruments and uniforms, with the promise that he'll teach the kids how to be musicians.
Once he's collected his bankroll, Hill skips town, leaving the kids in the lurch. Looking for new suckers in Iowa, Hill arrives in River City, where he declares that the only way to save the youth of River City from the lure of the poolroom is to organize a boy's band.
He charms the mayor's wife Eulalie (Hermione Gingold) into forming a ladies' dance committee and sets his sights on winning over local music teacher Marian Paroo (Shirley Jones). Marian rightly considers Hill a fraud, especially when he espouses the Think System of learning music: if you think a tune, he claims, you can play it.
But Marian becomes Hill's staunchest ally when her young brother Winthrop (Ronny Howard), sullen and withdrawn since the death of his father, exuberantly comes out of his shell at the prospect of joining Hill's band; and Marian's budding romance with the charming but unreliable Hill ultimately brings her out of her own shell as well.
Marion Hargrove's script uses most of the original play, with a handful of amusing expansions, especially in the roles played by Gingold and by Buddy Hackett as Hill's comic sidekick.