In Conviction, brother and sister Kenny (Sam Rockwell) and Betty Anne Waters (Hilary Swank) have the kind of fierce devotion to each other more often seen in movie lovers or mafioso. Their connection is undoubtedly forged in a difficult childhood: a negligent mother, nowhere-to-be-seen fathers, and a painful separation courtesy of the foster care system. A born troublemaker, Kenny has been stealing penny candy and breaking into neighbors’ homes since childhood, but nothing he does can diminish his sister’s love. As played by the tremendously likable Sam Rockwell, who has built a career impersonating goofballs and weisenheimers, Kenny is both obnoxious and lovable; one of life’s misfits doomed to repeat the same mistakes again and again and skilled at setting law boys’ teeth on edge.

When grown-up Kenny is arrested for murder and sent away for life, the strange-but-true crux of Kenny and Betty Anne’s story kicks in. His sister, who has a husband and two young children at home, decides to single-handedly get her brother out of prison. She enrolls in law school and, over the course of 18 years, works to have him exonerated.

The only certainty is struggle and Betty Anne has her fill of it, working nights in a bar while struggling through class each day. Betty Anne’s sidekick in this lonely crusade is fellow law student Abra Rice (Minnie Driver), a mouthy type who distracts us temporarily from the fact that Betty Anne — as presented in Conviction — is an empty husk of a woman and a bit of a yawn. We’ve also seen this Hilary Swank before, the blue-collar scrapper determined to succeed against all odds a la Million Dollar Baby. And we’ve seen shades of this character before too: the impassioned woman with a cause in Silkwood or Erin Brockovich. But while those films gave us some semblance of real, flawed, interesting women, Conviction imagines Betty Anne as a virtual saint doing battle for her brother. She comes across as scarily obsessive, with no inner life to illuminate her compulsion. The “colorful” ancillary characters, with their quirky “humanity,” only underscore the point that Betty Anne is not quite flesh and blood. They are a collection of wisecracking sidekicks like salty Abra, a familiar type from vintage women’s pictures, and gothic proletariats reminiscent of Coen Brothers’ characters played straight. These include the glad-she’s-back, oddly enjoyable Juliette Lewis as a snaggletoothed harridan ex of Kenny’s who helped send him to the Big House, downing glass after glass of cheap wine. She’s like a pesky dandelion poking through the glum sidewalk of the picture.

There are obstacles placed in Betty Anne’s way: the evidence she needs to exonerate her brother on DNA grounds has disappeared and she’s facing a district attorney more interested in politics than justice. But all the obstacles are external ones, and it appears Betty Anne herself never has a moment of doubt about her crusade despite a momentary wallowing in bed when she gives up custody of her two sons so they can live with her ex-husband. It is probably more the faults of director Tony Goldwyn and writer Pamela Gray than Swank’s: She has no apparent foothold for burrowing into this material in any emotional or psychological way.

Goldwyn has spent the bulk of his career in television and, frankly, it shows: there is a flat, matter of fact, artlessness to his mise en scene and to his characters, who seem to have had their precious bodily fluids drained all in the service of telling this astounding story.