I Used to Be Darker  (opening Thursday [August 7]) is the kind of film that seems to tell its story sideways. When Northern Irish teen Taryn (Deragh Campbell) shows up at her aunt’s house in Baltimore, we know she’s pregnant and emotionally lost, but little else. And we know that she’s landed there in the middle of a bitter separation between her aunt and uncle—whose college-age daughter Abby (Hannah Gross) isn’t taking the new arrangement very well—but we never really find out why.

In the midst of all this, through long and often quiet set pieces that offer little in the way of exposition, we come to experience the frustration and sadness of a family on the ropes.  “A lot of it’s about misdirected anger,” says Toronto-native Campbell, her Irish accent now jarringly gone when she speaks to the Straight from New York. “Abby’s mad at her parents but it gets directed at me [Taryn] at one point. A lot of movies have these direct channels of communication that aren’t always there in real life.”

Besides its highly naturalistic approach, much of the film’s power lies in the unexploded tensions between characters whose bonds have been ravaged. Abby’s parents Bill (Ned Oldham) and Kim (Kim Porter) are just as capable of wearily sharing a whiskey as they are trading barbs. Campbell notes that writer-director Matt Porterfield benefited greatly from his unusual approach to casting, with both herself and her real life friend Gross scoring their first film roles. Oldham and Porter, like their characters, are both musicians.

“He’s really good at seeing how people will go together, how they’ll look together, how they behave together,” Campbell says.” And for me, one of the big achievements of the film is how we really do seem like a family.”

Campbell credits her director for the “communal” vibe he established on set, while Gross, joining in on the call, describes the whole experience as “dreamily isolated.”

“But there was also this feeling, this tangible, magical feeling about it that something really special was happening,” Gross continues. “This feeling that what was happening in the moment must translate into something further on.”

What happened “further on” was the emergence of a festival and critical hit that cost roughly $50,000 to make. A miracle, by any standard.  Adds Campbell, with perfect succinctness: “It’s, like, this quiet movie but it’s also this unstoppable force.”