Tully: Charlize Theron proves motherhood is not for sissies

After two serious missteps – the barmy Labor Day and the misguided Men, Women & Children – Jason Reitman reunites with Diablo Cody, writer of his breakthrough Juno, to give us something we didn't know we wanted: a mash-up of Mary Poppins and We Need to Talk About Kevin.

Tully invites the audience’s indulgence. The story apparently hangs around first-world solutions to whole-world problems. At least one of the screenplay’s narrative switchbacks has been too-often manoeuvred.

Some mental health advocates have been uneasy with the heightened treatment of postpartum depression. None of those clanks or hisses can, however, conceal the sincerity of Cody’s intent. She’s here to confirm that motherhood is not for sissies.

Played by a terrifically distraught and significantly rounded-out Charlize Theron, Marlo, middle-class wife to a striving husband (Ron Livingston), first enters the screen belly-first in a state of advanced pregnancy.

She already has a lot on her plate. Her daughter is beginning to feel pressure from the image fascists. Her young son, who appears to be on the autistic spectrum, is annoying the patronising teachers at his school and is on the point of being euphemistically ejected. “We love, Jonah. He’s . . . quirky,” they say.

Marlo isn’t having it. “Do I have a kid or a fucking ukulele?” she snorts back. Reitman exploits a canny sound design – the hammering of tiny feet against car seats is particularly grating – to heighten the racket that children make when a parent is trying to accomplish hitherto uncomplicated acts like breathing. Everything that’s not stained is broken.

Cody is equally good on the way Sartre’s Other People contribute to the hell of parenthood. A supposedly helpful, shamelessly judgmental older woman frowns at Tully for drinking even decaffeinated coffee.

At least she can get away from strangers. There is no escape from her successful brother and his passive-aggressive, wellness-touting wife. (It’s decent of the film-makers to satirise exactly the kind of people who go to see their films.)

The in-laws suggest paying for something called a "night nanny". Little known outside the world of kings and Microsoft CEOs, such people apparently remain awake with the baby and, if he or she wakes, discreetly slip tiny mouth beneath maternal breast. Initially resistant, Marlo eventually gives in. Fair enough. We wouldn't have a film otherwise.

The script does admit that the arrangement is unspeakably “bourgie”. No normal person could hope to afford such a person. (Heck, why not go the whole hog and hire a wet nurse?) But the conceit does, by showing us a before and after, allow discussion of what women lose in the post-natal confusion.

Tully (Mackenzie Davis, apparently effortless), the young woman who takes the job, really is a modern version of Mary Poppins. She is tireless. She is cool. She gets on as well with the children as she does with a suddenly liberated Marlo.

Certain moments may grate with northern Europeans. “Why don’t you talk about it?” Tully says, apparently aghast, when Marlo explains that she and her husband no longer have sex. “Because we’re not bleeding Americans,” some of us long to reply. Obviously, the protagonist doesn’t.

Not everybody will buy the jarring ending, but the film plays fair with its audience. All the bits fit together. Thank Cody’s consistently witty script. Thank Reitman’s gently propulsive direction.

And thank Charlize Theron. Even with the pounds piled on she looks like only Charlize Theron can. It is, rather, her deflated posture and the leadenness of her gestures that really sell the performance.

“What’s wrong with your body?” her daughter asks. It seems like a fair question at the time. Theron’s ability to convey physical defeat through bearing alone deserves an Oscar nomination. She may well get one.

In cinemas from May 4th