In Peter Hedges' “Ben Is Back,” the titular 19-year-old living in a sober living center makes a surprise visit to his family on Christmas Eve. His mother, Holly, played by Julia Roberts (in one of her strongest performances in years), is overjoyed, hoping against hope that this is signals that he is breaking free of the opioids that have devastated his life, his family and the lives of others.

His stepfather Neal (a nuanced Courtney B. Vance) is less trusting, having bankrolled Ben’s multiple attempts at rehab and pointing out, with a note of earned bitterness, “If (Ben) were black, he'd be in jail by now.”

Ben’s sister Ivy (Kathryn Newton) isn’t crazy about this either. But Ben (played by Hedges’ son Lucas) swears this time is different, even as he admits his family has no reason to trust him or any other junkie.

And yes, Peter Hedges, still perhaps best known for the novel and screenplay “What’s Eating Gilbert Grape?” didn’t necessarily have his son in mind for the part. He had directed his son once before, 11 years ago, in “Dan in Real Life.”

Since then, Lucas, who just turned 22, has been on a dazzling hot streak, from a star-making turn in “Manchester by the Sea” to well-regarded roles in “Ladybird,” “Three Billboards Outside Ebbing, Missouri” and “Boy Erased.”

“I wrote a role that I hoped he would want to play were I not his father,” Hedges said recently. “The reason I say that because he'd been clear, and not in a mean way, that he wanted to keep his work separate from our relationship — ‘you be my father and I'll go be an actor in other people's films.' I didn't imagine he would be in it.”

Fortunately, Hedges says, he had an ally in Roberts.

“When Julia read the script and I met with her, she said Lucas was the only person she wanted to do the film with. Julia began a very, I think, sweet and persuasive. ...” He pauses. “I wouldn't call it a campaign, but she lobbied for him to do the film. The idea of working with her was super exciting for him. But I also think Lucas likes to do projects that he thinks have purpose more than just maybe entertainment. I really believe he believed in this story.”

“Ben Is Back,” which opens Friday in Austin, has its roots in Peter Hedges' real-life experiences with addiction and its consequences.

“About four or five years ago, a close friend overdosed and died, my favorite actor ever (Philip Seymour Hoffman) overdosed and died, and a relative nearly died,” Hedges says. “I knew I wanted to write about the heroin and opioid epidemic in some way, but I didn't know what that would look like.”

Hedges knew how these stories could play out. “I am the son of an alcoholic, and I grew up in a family that was ravaged by alcoholism,” he says. “I wanted to write something to try to make sense of what was happening and to put something in the world that would be a part of a conversation about what we start to do to turn this tragic situation around. That was my broad idea.”

Then Hedges began a period of intense research. “I just was obsessively reading every book, every article, going to meetings, talking with people in recovery. I just filled my walls with pictures of people who we'd lost, people I don't know, their faces.”

Hedges decided the problem was too big to tell multiple stories. “I decided I would write about one family over the course of one day,” he says. “I love writing about families, and since I come from a family where every family member was impacted by my mother's alcoholism, it was, I think, a natural jumping-off point for me.”

It’s impossible to look away from Lucas Hedges when he is on the screen. He has to walk a tightrope — he knows if he is clean or not, but neither the audience nor his family members know what is going on. It’s extremely impressive to watch.

“I'm knocked out by him,” Peter Hedges says. “Obviously, he's my son, but you can love your child and not think they're the greatest at whatever they love to do. I went to the little league games; I never thought he'd be pitching for Mets. He is, at a young age, acting opposite the best actors we have and holding his own. I'm very proud.”