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When her 19-year-old son arrives home unexpectedly for Christmas, Holly feels happiness — and several other emotions, each of which plays eloquently across her face. Holly welcomes him, then quickly hides all the pills and jewelry in her house. The prospect of Ben being back is, apparently, an alarming one.

It quickly becomes clear that Ben (Lucas Hedges) is a recovering addict, and lots of people will be even more conflicted about seeing him than his mom (Julia Roberts) is. These skeptics include his younger sister (Kathryn Newton) and his stepfather (Courtney B. Vance), as well as other figures who will be introduced when the movie shifts from a seriocomic story of a blended family to a thriller about the mean streets of suburbia.

Like the titular protagonist of the recent “Beautiful Boy” — a young addict played by Timothée Chalamet — Ben has two younger half-siblings who adore him. That’s not the only similarity between the two addiction dramas, which are as closely linked as the brilliant careers of Hedges and Chalamet. (Both actors played disappointing boyfriends in last year’s “Lady Bird.” Lately, they seem to have divided all the top troubled-youth roles between them.)

Where “Beautiful Boy” meandered back and forth through past and present, “Ben Is Back” takes place over the course of a single day. Writer-director Peter Hedges (Lucas’s father) doesn’t trifle with flashbacks to prove that his title character was once a great kid, or to reveal where things went wrong. The tight time frame gives the movie a welcome urgency, but it doesn’t prevent its second half from becoming lurid and melodramatic.


Roberts’s performance is complex and winning, even if Holly is not an entirely believable character. (Mark Schafer/LD Entertainment/Roadside Attractions)

It turns out that Ben didn’t just steal from his family and introduce his friends and lovers to potentially deadly narcotics. He also trafficked with dealers who now think he still owes them something. To get his attention, they kidnap the family dog, Ponce, while everyone is at church — on Christmas Eve, no less.

Ben and Holly set out to rescue Ponce, a question that also revisits the addict’s worst moments and his least admirable acquaintances. Concerned for the safety of his mother, Ben manages to ditch her. But that just means that Holly must now pursue both her son and the pooch. She’s not about to abandon either one.

Roberts’s performance is a complex and winning one, even if Holly is not an entirely believable character. Her Tiger Mom adventures are implausible, although they’re still more convincing than the harangues she delivers against two stand-ins for the pharmaceutical industry: one a doddering physician and the other a clerk at a drive-through pharmacy. Holly seems intent on embarrassing the opioid crisis out of existence, a strategy that feels as futile in the movie as it would in real life.

There are some authentic moments scattered through the second act, notably, Holly’s poignant encounter with a woman (Rachel Bay Jones) who has lost her daughter to dope. But after Ponce vanishes, most of what happens is a distraction from the story’s more cogent first half. Ben’s clashes with his mistrustful family members are painful enough. Did the movie really have to go after the dog, too?

R. At area theaters. Contains coarse language and drug use. 103 minutes.