Theron, Davis breathe life into ‘Tully’

Is “Tully” an unusually hard-edged family dramedy or straight-up domestic horror flick?

A few parents might find themselves wondering not long after Marlo (a terrific Charlize Theron), who doesn’t seem to have slept in years, gives birth to her third child.

As the 4 a.m. feedings begin (again), the director, Jason Reitman, unleashes a tour de force montage that seems to last minutes, if not hours, a rapid- fire assault of leaky nipples and discarded diapers: Pump, nurse, change, toss, repeat. You’ll laugh, you’ll cringe, you’ll reach instinctively for your wet wipes.

The s t ory actually begins a few days before Marlo goes into labor, letting us observe the cycle of drudgery that her life has become. Her husband, Drew ( Ron Livingston), is a genial semi-presence, either away on business or away at his video games.

He’s little help to Marlo in raising their daughter, Sarah (Lia Frankland), and their son, Jonah ( Asher Miles Fallica), whose emotional difficulties are getting noticed at school. When Jonah throws a fit in his pregnant mom’s car, screaming and kicking at the back of her seat, the movie gives Marlo’s despair an eerie psycho- thriller vibe, like something out of “The Babadook.”

“Tully,” in other words, may not be everyone’s idea of an evening’s entertainment, particularly those who require escapism: It’s one of the more viscerally accurate portraits of parenthood, and specifically motherhood, that the movies have recently given us.

SHE NEEDS TO SLEEP

In “Tully,” Theron doesn’t dispense with her natural charisma so much as rough it up, giving it a hard, bleary- eyed intensity. When Marlo gets pushed too far and finally vents, casting off her zombie- like exhaustion and belting her rage to the skies, you almost want to applaud her restraint; the vengeful warriors of “Mad Max: Fury Road” and “Atomic Blonde” seem apt to materialize on the spot.

Marlo is so clearly burning the candle at both ends that her wealthy brother, Craig (Mark Duplass), tactfully acknowledging her past struggles with postpartum depression, offers to pay for a night nanny. Marlo is ini- tially reluctant to welcome a stranger into her home, but after she has the baby — in one of the most deliberately perfunctory childbirth scenes ever filmed — it soon becomes clear that something’s got to give.

Enter t he s erenely smiling Tully (Mackenzie Davis), a twentysomething sprite of a woman who arrives at the house each evening, takes firm hold of the baby and sends Marlo off to bed, waking her only for nighttime feedings.

With her soothing yet forthright manner, her wide eyes twinkling with reassurance and mischief, Tully has the affect, and the seemingly magical powers, of a woodland nymph. Marlo awakens each morning to find the nanny gone, with only the precious gift of a spotless house or a plate of freshly baked cupcakes to suggest she was even there.

“I’m here to take care of you,” Tully tells Marlo, and it’s in the layered mystery of that sentiment that the movie stirs to life. In terms of age and experience, the women could scarcely be more different. But they also have more in common than meets the eye, and Tully turns out to be both a fount of precocious wisdom and an insidiously good listener.

Before long she has Marlo laying out the details of her nonexistent sex life with Drew and delving into her own more free-spirited past, long before she ever dreamed of settling down. At which point, the movie stops being strictly about the anguish of parenthood and turns into something more broadly bittersweet, a despairing reflection on the road not taken.

MATURING ON-SCREEN

At times “Tully” plays like the third installment of an unofficial series that began with “Juno” and continued with “Young Adult.” The result is a kind of trilogy on the pitfalls of suburban domesticity, moving from teenage disillusionment to stunted adulthood to the onset of middle-age misery, each stage marked by easy laughs and hardwon epiphanies.

It’s probably no coincidence that nearly everyone in Marlo’s orbit keeps referring to her son as “quirky” — a strange euphemism for behavior that suggests Jacob might be on the autism spectrum. Reitman, for his part, undercuts the habitual slickness of his filmmaking by moving the camera around more vigorously than usual, especially in Marlo’s home, as if to enhance the feel of domestic clutter.

But the movie really comes together when Tully swoops i n. The vibe becomes faintly otherworldly; her conversations with Marlo take on a lilting, almost musical rhythm. Davis, whom you may recall from “Blade Runner 2049,” has a wondrous stillness to her; simply by watching and listening, she gently recalibrates Theron’s rhythms, drawing out everything within Marlo that life has threatened to snuff out.

Their relationship is so incisively drawn that it’s a shame the movie doesn’t build to an ending worthy of them; the one dreamed up leaves you with more questions than answers. In my own imagination, “Tully” concludes on a less-calculated note, which I mean less as criticism than as rueful acknowledgment of the movie’s central insight.

FOCUS FEATURES Charlize Theron in “Tully.”