“Conviction” is based on an inspirational true story of resolute dedication and dogged persistence in the face of monolithic cultural and societal odds.

The film’s title, a smart double-entendre, suggests a story of righteous tenacity, the sort of fantastic narrative that you might be tempted to dismiss as fiction were it not true. While “Conviction,” directed by actor Tony Goldwyn, is a fairly rote, mechanical cinematic procedure, it is well-carried by its intrinsically remarkable plot and several Oscar-caliber performances.

In 1983, Kenny Waters (Sam Rockwell) was arrested for the gruesome murder of a middle-aged woman in a small, backwater Massachusetts town. Though he maintained his innocence, Kenny’s appeals fell on deaf ears and he was sentenced to life in prison.

Convinced of his innocence, his sister, Betty Anne (Hilary Swank), a housemom and high school dropout, decided to do what no one else could or would — she earned her GED diploma, went to college, and followed it with law school — all while working nights in a bar and keeping her family (not always successfully) afloat.

Betty Anne would battle setback after setback, challenging both misapplied evidence and police corruption in a single-minded obsession to free her brother. And it took only 18 years.

Because “Conviction” is largely by the numbers, it succeeds or fails based on its cast, and luckily for the film, the cast is top-notch. Remember when Rockwell was a comic actor and a darn funny one? Thank goodness he is an exceptional dramatic actor as well. Rockwell gives us a man we like but aren’t sure we can trust.

Swank, who is certainly a smart enough actor to know Oscar bait when she sees it, turns in a fierce, stalwart, largely solemn performance. There is no doubt that Swank’s Betty Anne is Massachusetts white trash, born and bred. But that makes her more interesting than a milquetoast, middle-class character, and certainly makes her achievement that much more admirable.

Some of the finest performances in the film come from the supporting cast, particularly Juliette Lewis, who may also see a gold statue in her future for her role as one of Kenny’s jilted, classless ex-lovers.

Unquestionably inspiring and certainly not without the power to both rouse and coax tears, we nevertheless get the impression that there is an even better film here, clamoring to get out. Perhaps in the hands of a more experienced director, “Conviction” could have been something truly great.

However, while familiar and conventional, that doesn’t mean it can’t also be formidable. “Conviction” is earnest, it is stirring and ultimately, it delivers.

CONVICTION

Cast: Hilary Swank, Sam Rockwell, Melissa Leo, Minnie Driver, Juliette Lewis, Clea DuVall, Bailee Madison, Tobias Campbell

Director: Tony Goldwyn

Rated: R (for language, violent images)

Running time: 1 hour, 47 minutes

Photo by Ron Batzdorff / Fox Searchlight