David Gordon Green’s “Undertow” opens the same way his beautiful “All the Real Girls” did, with two teens in love gazing at each other and sharing whispered conversation. But in short order the film turns away from Green’s usual style of atmosphere and character drama and develops, of all things, a plot.

The results are not completely successful. Green’s strengths are not in telling stories but in painting pictures and evoking moods. But “Undertow” often manages to have it both ways, to show a compelling storyline and to be contemplative. Sometimes the mechanics of the plot serve the greater good by putting the characters into situations in which Green’s writing and directing skills can be put to truly excellent use.

It is set in rural Georgia in what could either be today or 25 years ago. A widower named John Munn (Dermot Mulroney) has a tiny farm and two sons, 16-year-old Chris (Jamie Bell) and 10-year-old Tim (Devon Alan). Chris is the Romeo we saw at the beginning, just prior to his being chased away by the girl’s father on account of Chris being a no-account — a barefoot no-account at that, which proves to be a liability when, in his flight, he steps on a board with a nail in it.

Chris has been in and out of trouble since the family moved to the boondocks following their mother’s death. Young Tim is in poor health owing to his having pica, a syndrome wherein victims compulsively eat non-food items. Tim has a particular fondness, if you can call it that, for dirt and paint.

Events are set in motion when John’s brother, the extremely no-account Uncle Deel (Josh Lucas), shows up for reasons he does not explain. We soon realize he wants his share of his and father’s collection of Mexican gold coins, allegedly worth thousands of dollars. The lengths to which he will go to get these coins are, to put it mildly, unsettling.

Chris and Tim eventually find themselves wandering through the backwoods of the South, taking care of each other and relying on the kindness of strangers when they can. Their relationship, well-played by Jamie Bell (of “Billy Elliot”) and Devon Alan, feels natural and real. Honest relationships are a hallmark of Green’s films, and this is no exception.

It is tempting to dismiss the whole lot of them as white-trash hillbillies, and I suppose that would be an accurate assessment. But the film succeeds in making them sympathetic, fully realized characters. They are fascinating to watch, not because they are different from the mainstream, but because they are, in spite of their differences, very familiar.

The urgent musical score by Philip Glass improves the film; in fact, I daresay most films are improved by a Philip Glass score. The cinematography, by Green regular Tim Orr, beautifully captures the rural environment and contributes greatly to the film’s overall feel.

That “feel” is ultimately what plants the movie firmly in excellent territory. The story itself, though occasionally compelling, is mostly just a means to an end, a way to show these particular people reacting to a series of events. It’s the people who are most interesting, not the things that happen to them. As with “All the Real Girls,” I found myself wanting to hang out in this world for a little while longer.

B+ (1 hr., 47 min.; R, a little profanity, one scene of fairly strong violence.)