A coming-of-age tale that’s also a suspense thriller, Jeff Nichols’ “Mud” continues the string of remarkable films the writer-director began with “Shotgun Stories” and followed with the stunning “Take Shelter.” At once ode to a vanishing way of life and homage to the Mississippi River masterworks of Mark Twain, this beautifully realized picture is easily one of the year’s best thus far.

Matthew McConaughey, bolstering the career resurgence he started with “The Lincoln Lawyer” and continued with “Magic Mike,” “Bernie” and “Killer Joe,” stars as the title character, a bedraggled miscreant on the run from the law for killing his love Juniper’s nasty Texas boyfriend. But the story is told from the perspective of Ellis (Tye Sheridan), a fourteen-year old who, along with his buddy Neckbone (Jacob Lofland), sneaks to an island in the Mississippi where it’s rumored that a boat has been left dangling in a tree after a recent flood. For Ellis, the trip takes him away from troubles at the family houseboat, where his father Senior (Ray McKinnon) and mother Mary Lee (Sarah Paulson) are going through a rough patch at least partially caused by the threat that they might lose their home.

The boys find not only the boat well above ground, but also Mud, who’s taken up residence in it to avoid police roadblocks and searches—as well as the private army the father of the man he killed has sent after him. Mud enthralls them with his tall tales, mysterious allusions to the magical properties of his lucky (indeed, only) shirt, and stories of his undying love for Juniper (Reese Witherspoon), whom he rescued from a terrible fate and is now desperate to reunite with. And they decide to help the charming reprobate, who treats them with a directness and respect they’re unaccustomed to, by bringing him food and material to repair the boat—and making contact with Juniper, ensconced in a local motel, to arrange for her to escape with him.

Of course their efforts bring them under suspicion from Senior and Mary Lee as well as Neckbone’s hound-dog Uncle Galen (Michael Shannon), who uses a home-made helmet to dive for mussels in the river. They also require Ellis to contact reclusive neighbor Tom Blankenship (Sam Shepard), who lives on a houseboat on the shore opposite his, a father figure to Mud who might be willing to help him. And, of course, they bring the lads unwanted attention from the extra-legal posse of the revenge-seeking King (Joe Don Baker). And in his few free moments Ellis becomes infatuated with a pretty older schoolmate, May Pearl (Bonnie Sturdivant), whom he grows so devoted to that he even puts himself at risk to defend her honor against a senior boy—a subplot that mirrors Mud’s crazed dedication to Juniper, and with a similar outcome.

The myriad of character and incident in “Mud” makes for a narrative of epic length, and Nichols, working in tandem with editor Julie Monroe, doesn’t rush its development. But the film doesn’t seem to dawdle or plod. Like “Take Shelter” it holds one’s attention easily, though with a very different vibe. You’re left not with a sense of impatience over the stately pace, but with an appreciation of its richness.

And admiration for the performances. One has gotten to the point of expecting the unexpected from McConaughey, who doesn’t disappoint. His Mud is an irresistible rascal—a charismatic, drawling master of redneck rhetoric, but also a sort of down-home knight without any shining armor who nobly springs into action when Ellis’ life is endangered… But still the film couldn’t work without the extraordinary performance of Sheridan, who doesn’t miss a beat in conveying Ellis’ changes of mood with a degree of expertise that would be the envy of many actors twice his age. Lofland doesn’t have the opportunity to exhibit a similar range, but is wonderfully natural as a less complicated kid who’s also more practical, dickering for Mud’s pistol as the price for his help.

Juniper is a less rounded character than Mud or the boys, but Witherspoon gives her a sullied beauty. Shannon, so extraordinary as the apparently unhinged protagonist of “Take Shelter,” shines in the virtually cameo part of Galen, and Shepard brings his customary sense of rugged authority to Tom, while McKinnon and Paulson texture the parts of Ellis’ parents, the former in particular bringing a sense of wounded pride to his character. Baker effortlessly captures the quiet viciousness of King, and milks to the utmost his moment of sad resignation at the close.

The performances are matched by the technical side. Cinematographer Adam Stone gives a poetic cast to the Arkansas locations without overdoing it, and Richard A. Wright’s production design is a model of authenticity with a touch of the magical, while David Wingo’s score lends local color without ostentation.

There’s a sort of familial relationship between “Mud” and David Gordon Green’s sadly underappreciated “Undertow,” though Nichols’ film is far less dark and forbidding—in fact, despite the seriousness of many of its themes, there’s an overall sense of lightness to it. One can only hope that it receives the attention that Green’s film deserved but never got. In cinematic terms it’s a breath of air as fresh as the breeze one can almost feel in its lovely final shot of the sea.