Loving an addict is a nearly impossible thing to do. Writer/director Peter Hedges captures the aching difficulty with a crystalline and harrowing clarity in “Ben Is Back.” It stars his son, Lucas Hedges, as Ben, and Smyrna native Julia Roberts as Ben’s mother, Holly, whose Christmas wish is to have Ben home for the holiday. It’s a lesson in being careful what you wish for.

“Ben Is Back,” set within a contained 24 hours, doesn’t need to show or overly tell us about Ben’s past. That’s communicated clearly in the extreme reactions the family has to his return. “Mom — stop,” is the first thing Ben’s sister Ivy says when they spot him in the driveway before Holly rushes to embrace him. Ivy is on the phone in an instant, contacting her stepfather, Neil (Courtney B. Vance). Everyone in the family is on edge. Holly demands a drug test if Ben is going to stay the night. These kinds of reactions tell us all we need to know to understand the extremity of the chaos Ben’s addiction has sown in the family.

Ben’s story is slowly revealed, piecemeal, as he and Holly embark on a Christmas Eve journey that turns into a dark night of the soul. First it’s to the mall for a church sweater, where Holly gets them kicked out of a department store for demanding to search his clothing for drugs. Ben is also spotted by old friends, setting off a chain of increasingly dangerous events, ultimately leading to a confrontation with someone from his past to whom he owes a debt.

The theme Hedges’ script hammers again and again is the flexible, fallible nature of honesty and truth. Ben professes that “rigorous honesty” is the only way he can get through the day — demanding to buy his own presents for his younger brother and sister — but Hedges plants seeds of doubt about Ben’s honesty throughout.

When Holly reaches out for help to a fellow mother of an addict, her friend says frankly, “We can’t save them, but we have to try.” This is the motivation that keeps Holly returning again and again, turning the car around. It’s codependency, and it’s unconditional love.

Roberts gives one of her most sensitive and searching performances yet, and her face is her most expressive tool — her wide grin at the sight of her son, her panic and despair at the smallest transgressions. She is sensational across from Hedges, who portrays Ben with a sense of haunted, plaintive anguish. He mourns his past, present and future, while his mother desperately tries to wake him up. Peter Hedges has crafted an exquisitely devastating family story for the opiate era that quietly asks us to do the same.

MOVIE REVIEW

“Ben is Back”

Grade: B

Starring Julia Roberts, Lucas Hedges and Kathryn Newton. Directed by Peter Hedges.

Rated R for language throughout and some drug use. Check listings for theaters. 1 hour, 43 minutes.

Bottom line: An exquisitely devastating family story that asks us to wake up