Suburban housewife Margo (Charlize Theron) is living in a hell we don't hear much about at the movies. She loves her two kids, but they're an exhausting handful: Sarah (Lia Frankland) is at a difficult age for girls, we're told (she's 8), and her younger brother, Jonah (Asher Miles Fallica), seems clearly to be autistic, although everyone tries to be nice about it and refer to him as merely "quirky." Making matters worse, Margo is pregnant again — as we see when her huge belly precedes her into the opening shot of "Tully," a movie filled with raw truths about the maternal condition and with a startling plot twist that suddenly rears up out of the story and transforms everything that came before it.

It's good to see Theron, giving one of her best performances in an exceptional career, reunited with director Jason Reitman and screenwriter Diablo Cody for the first time since the bitingly perceptive "Young Adult," a 2011 movie that never got the love it deserved. This one, with its bold treatment of a subject with which half of the moviegoing population will be at least glancingly familiar, should be more appreciatively received.

Margo lives with her husband, Drew (Ron Livingston), in a leafy small town outside of New York City. Drew is a good guy who's away a lot for work and doesn't grasp the depth of his wife's bleary despair. We do, though, as Reitman shows us around their home, a bomb site of kiddie clutter, and later stages a resonant scene in which little Sarah gets a glimpse of her mom's flubbery postnatal torso and asks, "Mom, what's wrong with your body?"

With the baby arrived, Margo's mental condition worsens. Her wealthy brother, Craig (Mark Duplass), offers her a gift: He wants to pay for a "night nanny" to begin an overnight baby-care shift so Margo can get some sleep. Margo resists Craig's offer ("This is like a Lifetime movie where the nanny kills the family"), but not for long. In a nerve-scraping scene, we see Margo and her kids inside the family car. The baby is shrieking and will not be appeased, and Jonah is acting out, furiously kicking the back of the driver's seat in which Margo is sitting. Something inside her snaps, and she erupts in a howl of anguish. Maybe a night nanny isn't such a bad idea.

One night soon after, Tully (an effervescent Mackenzie Davis) shows up at Margo's door. She's 26 years old and full of vim and sparkle. "I'm here to help you with everything," she says. Tully's abs, beneath a crop-top tee, are formidably tight (a physical state the 40-ish Margo remembers from her own receding youth), and she's a fount of lively chatter and obscure knowledge — about barnacles, astronomy, Japanese phrases. ("You're like a book of fun facts for unpopular fourth-graders," Margo says, although fondly.)

The morning after Tully's first tour of duty, Margo awakes — refreshed for once — to find that Tully has totally tidied up the house. On another morning, she discovers a big batch of fresh-baked cupcakes awaiting her. Soon Margo, who'd lost all confidence in herself, starts cooking again, and Drew is happy to see the kids aren't eating frozen pizza for dinner anymore. When Margo actually whips up a pitcher of sangria, Tully says, "See, you are a homemaker."

Tully decides that it's time to deal with a crucial problem in Margo's marriage — she and Drew no longer have sex. This leads to an eerie scene in which we realize that there's something going on in this movie that hasn't dawned on us yet. Then Tully calls for a road trip: she and Margo will drive in to Brooklyn to visit some of Margo's old haunts in younger, happier times. This sounds like a dangerous idea even as it's being proposed.

I'll say no more.

"Tully" has already drawn objections for its treatment of postpartum depression. Writing for the website Motherly, midwife and pediatric nurse Diana Spalding says that what Margo actually seems to be suffering from is postpartum psychosis — a much more serious affliction. She says the filmmakers "seem not to have consulted with a therapist to ensure that the topic was handled appropriately," and that "in not addressing the fact that Margo has a postpartum psychosis, the rampant problem of maternal mental health concerns is perpetuated."

Surely it would be good if more people could be made aware of this problem. But is it the duty of movies to do so? If "Tully" hadn't been made, would we even be talking about it?

Kurt Loder is the film critic for Reason Online. To find out more about Kurt Loder and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.