A documentary by Kimberly Reed. Unrated. Plays Friday, March 12, Sunday to Tuesday, March 14 to 16, and Thursday, March 18, at the Vancity Theatre

Even if this riveting documentary holds back some key information for as long as it can, no review of Prodigal Sons can avoid the central thrust of writer-director Kimberly Reed’s multiple returns to her hometown of Helena, Montana. She might have become a big, busty, outgoing broad since moving to San Francisco, but back in Big Sky Country she was Paul McKerrow, star quarterback and one of three troubled sons of a doctor who died young and a mother who put up with a lot.

Reed initially heads home, her even-tempered girlfriend in tow, in time for her 20th high-school reunion. The reaction of classmates who admired her as a boy is intriguingly openhearted—or maybe they just like having cameras around. But the important business is with her older brother, Marc, still suffering from brain damage he got in a car crash at age 21—although his troubles started before that. In fact, Marc was adopted, and the search for his real ancestry leads to a discovery amazing to both him and anyone with the remotest knowledge of Hollywood royalty.

This twist uplifts the oversized, difficult fellow, who starts noodling his naive piano pieces with extra joy. He even travels to Split, Croatia, to meet extended family, and appears in a film about his grandfather. But soon he’s back to his abusive, occasionally violent, outbursts directed at Kimberly, their mother, or youngest brother, Todd, who suffers here—narratively speaking—because he is merely gay, not maladjusted.

Despite Prodigal’s fixation on Marc’s seemingly bottomless well of crazy, it keeps coming back to Kimberly’s anxiety about acceptance. Her protestations sometimes feel a tad overdramatized, or at least underexamined. Still, with a family like this, she was bound to play for the back bleachers, whatever else she did.