Grade: B+

Melissa Leo gives a terrific performance as a mother struggling to provide a home for her two sons while their father is off gambling away the family’s savings in “Frozen River,” and the best part of Courtney Hunt’s film is the honesty of the domestic scenes between her and the older boy T.J. (Charlie McDermott). Their relationship, and the affecting way in which the two actors embody it—along with the authentically frigid ambiance of the U.S.-Canadian border setting—give the picture a realistic grounding that sticks with you even when some of the plot mechanics swing into melodramatic terrain.

Leo is Ray, who works as a clerk at a store near the Mohawk reservation on the St. Lawrence River. When her husband decamps with the money that will upgrade the family to a larger trailer home—the disappearance of which will also lose them their deposit on the new unit—she goes looking for him at the local bingo parlor, where she sees his car being driven away by an Indian woman, the undemonstrative Lila (Misty Upham). It transpires that Lila simply claimed the car when she saw its driver catch a bus for parts unknown; she intended to use it to smuggle illegals across the frozen river, Indian territory where U.S. law isn’t in force, and when Ray shows up to reclaim it, Lila tricks her into participating in a run. And as her financial desperation mounts, Ray comes back for more.

This suspense-driven portion of the script sometimes goes a bit awry—an episode involving a nasty thug (Mark Boone Junior) takes the level up a few too many notches, and another concerning a bag with an unexpected cargo inside strains (though doesn’t completely break) credulity. Some deadpan moments featuring a state trooper (Michael O’Keefe) don’t play exactly on target, either. But the performances of Leo and Upham are so well calibrated, and they work so nicely against one another, that the film makes its way over the rough spots, generating considerable tension in the process, allowing even for an ending that may not be what you expect.

And the characters’ family backgrounds enrich the smuggling plot rather than detracting from it. Lila’s backstory—she has, at it happens, a reason for needing money too—isn’t terribly well drawn, but it provides a glimpse into the larger Mohawk community that’s happily unsentimental and matter-of-fact. And the depiction of Ray’s home is insightful and true. Much of that depends on McDermott’s turn as a troubled but basically good kid who takes some unfortunate short cuts trying to play the role of man of the house, to both Ray and his younger brother (James Reilly). But that part of the scenario is played with becoming modesty, too—what might have been a throwaway scene at the close involving T.J. and a Mohawk woman he’s bilked in a credit-card scam has surprising potency simply because it’s staged without the unusual Hollywood fanfare.

Made without frills, “Frozen River” looks every bit the low-budget independent picture that it is. But Reed Morano’s cinematography captures the snowy, inhospitable climate perfectly, as Inbal Weinberg’s production design does the feel of the cramped, shabby places where people constantly on the edge have to live. And the film treats its characters without either condescension or cheap sentimentality. Like another small American picture, Josh Sternfeld’s “Winter Solstice,” it’s a modest film, but one that’s fundamentally truthful and compelling, with an almost European sensibility.