It’s the kind of phenomenon — a caprice of nature that is absurd but also wondrous — designed to enchant adventurous children like Ellis (Tye Sheridan) and Neckbone (Jacob Lofland), two Arkansas boys who discover the boat on an overgrown island in the Mississippi River.
They also discover the fellow who claims to own, or at least inhabit, the vessel, a leathery loner whose name is Mud.Mud is played by Matthew McConaughey in the latest in a series of surprising, intense and often very funny performances following his escape from the commercial romantic-comedy penal colony. “Magic Mike,” “The Paperboy,” “The Lincoln Lawyer” and “Bernie” are all very different (and differently imperfect) movies, but in all of them, and in “Mud,” Mr. McConaughey commands attention with a variation on a certain kind of Southern character: handsome but battered, charming but also sinister, his self-confidence masking a history of bad luck and trouble.
Ellis and Neckbone are a little afraid of Mud, but Ellis in particular is immediately drawn to him, taking his wild stories (“stretchers,” Tom Sawyer might have called them) at face value and adopting the man as a cause and a surrogate father. (Ellis’s actual dad, played by Ray McKinnon, is a stern and moody fisherman struggling with hard times and a failing marriage).
Mud, with only a pistol and a lucky shirt for protection, is hiding out on the island because some bad guys are looking for him, and because he is waiting to run away with the love of his life, a lady named Juniper (Reese Witherspoon). He needs some help acquiring food and getting messages to Juniper, and his new young friends are happy to oblige — Ellis because he has found a kindred romantic soul, Neckbone because he can make a deal for that pistol and have a little fun in the bargain.
Part of the wonder and some of the letdown of “Mud” is that a lot of what Mud says turns out to be true. Juniper shows up at a nearby town, and so does a fleet of black Cadillacs full of dangerous-looking dudes commanded by the great Joe Don Baker. Even without this intrigue, Ellis has the usual coming-of-age business to contend with: the tension between his father and mother (Sarah Paulson); his crush on a girl named May Pearl (Bonnie Sturdivant); and potential problems with his sidekick, Neckbone, who lives in a trailer with his wayward uncle, Galen (Michael Shannon).
Mr. Nichols’s screenplay is perhaps a little too heavily plotted, especially toward the end, when everything comes together neatly and noisily, but he more than compensates with graceful rhythm, an unfussy eye for natural beauty and a sure sense of character and place. What might have been an earnest, oversensitive, stereotypically Sundance-y piece of regionalist misery is leavened by suspense and jolts of laughter.
Some of this comes from Neckbone, who serves as Ellis’s comic sidekick, a cynical and pragmatic foil for his dreamy buddy. The two boys, whose faces register their contrasting temperaments — Mr. Lofland with his brush cut and Dennis the Menace features; Mr. Sheridan with his hooded eyes and downturned mouth — have been guided into exceptionally subtle feats of acting. The grown-ups (and I should add Sam Shepard, as an enigmatic neighbor of Ellis’s, to the names mentioned above) are mighty good too.
Mr. Nichols, an Arkansas native whose previous features are “Shotgun Stories” and “Take Shelter,” is very much aware that life on the Mississippi, now as in Mark Twain’s day, is characterized by boisterous humor as well as hardship and stoicism. (He reportedly asked his cast to read “Huckleberry Finn” during production.)
Though Mud’s desperation eventually begins to show, his wit never deserts him. Nor does the movie, even as it tilts toward a busy climax, lose its confidence that a good story is not just about some crazy stuff that happens but also about the voice that does the telling. And Mr. Nichols’s voice is a distinctive and welcome presence in American film.