Lucas Hedges, 22, by his own account, has two very loving, caring parents. They encouraged him to pursue his acting career when, in the seventh grade, he was discovered by a casting agent during a school play. They are astonished by every role he takes, marveling at his choices and the different characters he embodies that don’t resemble him at all. They showed up to his opening night on Broadway in Kenneth Lonergan’s The Waverly Gallery, and they already have purchased tickets for its closing-night performance in January.

So it’s a bit of a head-scratcher, even to Lucas himself, that he had no intention of ever starring in a movie directed by his father, the novelist and screenwriter Peter Hedges (About a Boy, What’s Eating Gilbert Grape).

“I don’t let [my parents] watch the monitors when they come see me on set,” Lucas said. “It makes me self-conscious. I didn’t think it would be helpful that somebody I don’t like watching me act—that I don’t like to know they are around when I’m acting—should be directing me.”

Lucas felt differently once he read his dad’s script for Ben Is Back, a searing portrait of a family torn apart by their teenage son’s opioid addiction. “Once I saw what he created, I thought, ‘Oh, this actually could be amazing,’” Lucas said. “Having him as my dad will serve me more than it would hurt me.”

To Peter, it was the outcome he didn’t even allow himself to imagine. “I wrote [the movie] hoping he would read it, and wishing he wasn’t my son, so he could be in it,” Peter said. “Because he was very clear that he did not want to be in a film with me.”

The fear of perceived nepotism or extra scrutiny was little match for Julia Roberts, who, immediately after reading Peter’s script, had assumed Lucas would be playing Ben opposite her role as Holly, the fiercely loyal, optimistic mother who is willing to go to extremes to save her son.

“Lucas gave me an enormous gift by being in the film, because it made Julia very happy,” said Peter. “I think she still would’ve done the film, and in some ways it might have been an easier film to make if I’d just been directing someone that I grew to love as a son, but who wasn’t my son. But it really made it very special . . . It was hard, but it was awesome.”

When I meet the elder Hedges, he’s visiting Los Angeles for a 10-day trip that coincides with the opening of his movie. That’s both good and bad. For one, he gets to stay in his favorite hotel, the Four Seasons, which was also where he stayed the week of the 2003 Academy Awards, when he and co-writers Chris and Paul Weitz were nominated for their About a Boy adaptation. Peter stayed across the hall from Lonergan, who was nominated that year for his work on the Gangs of New York original script. Peter remembers “bobbing in the swimming pool” with Lucas in his arms, talking to Lonergan, who 13 years later would cast his son in the Oscar-nominated Manchester by the Sea, for which Lucas received a supporting-actor nom.

“I’m at Sundance, watching Lucas’s life change as that movie played, because you could feel it in the room,” said Peter of seeing Manchester for the first time. “I didn’t recognize him in the film. I didn’t know that kid. I wanted to tell everyone around me, ‘I’m his father.’ But I wanted to explain: I don’t know that kid—that cocky, aggressive, alpha-male boy.”

Being away from home has its downsides, in particular the stress that comes with an opening weekend and the onslaught of criticism that accompanies it. (The reviews have been kind, with the film hovering at 82 percent on Rotten Tomatoes, and it earned about $20,000 per screen for an impressive debut.) And that’s hard for Hedges, a warm and joyful 56-year-old—picture Tigger in a business suit—who wrote Ben Is Back as a response to his close friend dying of a drug overdose, his niece almost dying of one, and Philip Seymour Hoffman passing away in 2014.

“I vowed that I need to make something that endeavored to make some kind of [sense] of all this untenable loss,” Peter said.

Ben Is Back feels lived in, and has received praise from those who have dealt with addiction themselves, or have experienced it with family members. The film gets so many things right: the fear when Ben comes home from rehab early; his family’s trepidation around him; his mother’s fierce, irrational love that manifests in her willingness to throw away all reason in her quest to save him.

The Hollywood Reporter writer Chris Gardner, who is now almost nine years sober, recently reviewed the slew of addiction-centric films that bowed this awards season, including Beautiful Boy and A Star Is Born, and wrote this about Ben Is Back: “It’s about family, forgiveness, skeptical relatives, and where to place the blame for America’s urgent opioid crisis . . . And the 12-step meeting featured in the film is the most authentic one you’ll see. It manages all of this without ever feeling preachy.”

Peter had set out to make a movie as personal as his 2003 directorial debut, Pieces of April, which he watches, most often with Lucas, every Thanksgiving when it shows up on TV. That film, which stars Katie Holmes as a daughter who invites her estranged family, including her dying mother (Patricia Clarkson), for one last Thanksgiving dinner, was Hedges’s tribute to his own mother, an alcoholic who walked out on him and his siblings when he was seven years old, and didn’t return until he was a teenager. When she did, she became a social worker and dedicated her life to helping others.

“My mother’s sobriety—that’s when I found the theater, that’s when I moved from being a basketball player to being a musician, to being an actor, to then being a writer,” Peter said. “That’s when my life opened up in unimaginable ways.”

Peter writes most often about people’s capacity for redemption. It’s fueled his successes—Gilbert Grape, April, and About a Boy—but also his lesser-known work, including the Steve Carell-starrer Dan in Real Life, and The Odd Life of Timothy Green, the ill-fated 2012 film about a married couple (Jennifer Garner, Joel Edgerton) and their quest to bear a child. But Peter has reached a touching, personal symmetry with Ben Is Back, where his mother’s grandson is the one playing the addict in the film.

“There were moments when I’d look at Lucas, and it was so powerful that [my mother] Carole had her grandson [in this role],” Peter said. “I cried [on set] every day.”

For Lucas, the time he spent on set was rewarding, but not because he learned more about his dad—his father “was emotionally available to [him] since birth”—but because he saw him demand things he didn’t expect: another take, a different approach. “My dad has always been blinded by how amazing he thinks his kids are,” said Lucas. “And I was worried that he would be too easy to please. He had a high standard for me, and I was very impressed by that—his ability to stand by what he wanted for the film and not be a hyperbolic, easy-to-impress father.”

Lucas had very little time to prepare for the role. He came straight off filming Boy Erased to Ben Is Back, and therefore had to rely heavily on his father to guide him. But he’s now come to realize the magnitude of what they’ve taken on.

“When I was doing The Late Show with Stephen Colbert, a man came up to me and said that Carole, my grandmother, saved his life,” Lucas said. “That was the thing about her: she dedicated her life to service. It feels very poignant that I got to tell this story . . . Addiction runs deep in our family, and I felt like by carrying this story, I could help be of service to our family, both moving forward and today. It wasn’t even entirely for the world as much as it was for us.”

— The 10 best movies of 2018

— A whole new look at Apollo 11

— The Game of Thrones secrets in George R.R. Martin’s final script

— Sandra Bland’s sisters are still searching for answers about her death

— How a movie producer and Hollywood invented a right-wing commentator

Looking for more? Sign up for our daily Hollywood newsletter and never miss a story.