Julia Roberts is on a mission — again.

In a throwback to her scantily clad, door-knocking role in “Erin Brockovich,” she plays a drug addict’s determined mother in “Ben Is Back.” And she’s just as good without the smile.

Swell, too, is the sweet and subdued Lucas Hedges as her son Ben, who leaves rehab unannounced for a surprise family holiday. But within hours of arriving at his suburban New York home, he encounters destructive forces from his past, and gets sucked back into a dangerous world.

It will take a mom to save him.

“Ben Is Back” is the second movie this year about a young addict. It follows the overly pretty “Beautiful Boy,” which starred Timothée Chalamet, but it’s a lot better. For one, its setting is more realistic, set as it is in a tiny town that closely resembles those being ravaged by the opioid crisis. Nor does it shy away from showing the ugliness of addiction: the needles, the lying, the body searches.

Although “Ben” can get a little sentimental at times, Roberts and Hedges are a team to root for.