You know what's the absolute worst, is when a movie that has been doing rather well for itself suddenly makes just a little tiny shift, and you become fully aware that it's heading in a direction that will not work out well for it. But unlike regular bad endings, where the film abruptly pukes out, there's still enough plot left when that shift takes place that you have a lot of time to really think about how the movie is disintegrating, and watch helplessly as it keeps charging towards its horribly misjudged close. 2013 already had one of those movies, in The Place Beyond the Pines, and now it has another with Mud, which like that earlier film is an indie movie study of masculine self-identity, and which, to be fair, doesn't become nearly as broken as its third act rattles into pieces. It's still a pretty rough conclusion, though, which is horribly sad, because up till just past the three-quarter mark, Mud is one hell of a nifty psychological fable.

Pre-release buzz and the title of the film notwithstanding, Mud is not about Matthew McConaughey's eponymous drifter, hiding out on an island near the Arkansas/Texas border. In fact, though Mud is the prime mover of the plot and a constant shadowy presence even when he's not onscreen, the film's emotional arc sits entirely on the shoulders of Ellis (Tye Sheridan), a 14-year-old boy living on an ancient houseboat with his dissolute fisherman father (Ray McKinnon) and snappish, put-upon mother (Sarah Paulson), and to avoid his wearying home life, spends every summer day out in the watery places of Arkansas with his friend Neckbone (Jacob Lofland). One day, they're on the hunt for to find a spectacular sight in the woods - a powerboat that managed to make it dozens of feet above ground in a tree - when the stumble across the tight-lipped Mud, who without even at first offering his fake name, convinces the boys to help him out by bringing supplies the island, while he waits for somebody to show up.

Details trickle out, and before too long we can start putting things together: Mud killed a man to protect his on-and-off girlfriend Juniper (Reese Witherspoon), and he's hiding from the cops until he can scrounge together the spare parts to fix the boat and escape to Mexico with her. Neckbone responds to this out of an unfocused sense of respect for a fugitive badass, but for Ellis, this has a much more romantic element: he manages to convince himself that helping out Mud and Juniper will be contributing to a torrid, Romeo and Juliet-like situation where he's enabling a pair of tormented lovers to escape to their paradise.

For it's not really the boys' attempt to help Mud escape that drives the movie, though it's what drives the plot. Mud, for most of its running time, is about how a teenage boy who's actively trying to figure out this mystifying thing called "girls" for the first time absorbs the lessons that the grown men around him project. Meanwhile, the women in Ellis's immediate life - Juniper, his mom, and the high school girl May Pearl (Bonnie Sturdivant) that he's crushing on - at once both subvert and reinforce the sexist framework that the adult men are spouting off.

Mud could be rightfully accused of presenting an incredibly one-sided view of gender politics, with the women in the film being barely fleshed-out enough to qualify as two-dimensional, though this ends up having a lot to do with the film's resolute commitment to Ellis's POV. Besides, it's hardly the case that the film is terribly interested in digging into any character, besides Ellis himself and the projection of ideal manhood he ascribes to Mud. This is a largely symbolic film, not at all a realistic one, and this is a mode that writer-director Jeff Nichols does a fantastic job of exploring, even though it gets to be annoyingly schematic how each and ever adult male in the film ends up having the Statement of Beliefs that sits wrong with Ellis somehow, until his mother gets here own Female-Based Counter-Argument that doesn't necessarily sit any better, but at least manages to shock him out of the self-deluding frame that he's been clinging to for an entire feature, and presumably, an entire childhood.

There's a whole lot of early David Gordon Green in the film's slow-moving, minor-key exploration of place: Nichols and cinematographer Adam Stone do a better job than any filmmakers have since at least Green's own Undertow in using the sticky, sunblasted and plant-filled landscapes of the American South as a visual expression of character, and the absolutely gorgeous exterior cinematography crafts a romantic overlay for battered, impoverished settings that exactly matches Ellis's own half-awareness of the shortcomings of the adult worldview he's trying to adopt. It's a film to evoke the heat of summer, though it fantastically depicts the humidity, an all-encompassing dampness that saturates every location and character and suggest the omnipresence of rot.

There's a hell of a character piece that the film has going, then, with uniformly great performances (Sheridan and Shepard are the best), though the women in the cast get very little to do (I can't explain Witherspoon's presence in a nothing role, except by recourse to the idea that her career is on the skids and she needed to work with a respectable indie director). But the problem with it, is it's not able to head to anything concrete; the film is depicting a mental process, not a narrative one. So, at a certain point, Nichols has to fully commit to the "Mud is a fugitive" subplot, sending the film into a disjointed and trite series of climactic scenes that have as their best justification a really swell Joe Don Baker cameo. But even that isn't nearly enough to excuse how junky and broad the film abruptly turns, and how much it trivialises the conceptual, psychologically abstract opening and middle by putting Ells on the back burner and trotting out a gun battle that fits with the rest of the movie not remotely, and ends in a deeply cloying final scene.

It's such a disaster of a final act that it makes it hard to say if Mud ever actually knew what it was on about, or if the delicate sketch of an adolescent boy trying to fix his sense of sexual identity was just an accident. Certainly, it means that one leaves Mud with the very worst parts freshest in memory, and that's not something that any movie should ever do. For a long time, I was convinced that I loved the movie, and in the final crush, I didn't even like it; a huge drop but a decisive one, and it's hard to decide whether the fact that most of the movie is truly strong actually ends up mattering very much.