TULLY (15, 96 mins)

Starring: Charlize Theron, Mackenzie Davis, Ron Livingston, Mark Duplass, Asher Miles Fallica, Lia Frankland, Gameela Wright. Director: Jason Reitman.

Mother doesn't know best - she is teetering on the precipice of a nervous breakdown in Jason Reitman's beautifully crafted and bittersweet portrait of modern parenthood.

The third collaboration between the Montreal-born director and screenwriter Diablo Cody, who won an Oscar for her exemplary script for Juno, conceals poignant home truths behind trademark snappy dialogue and a mistimed sleight of hand that leaves a satisfying lump in the throat.

There is undeniable pleasure in unravelling the many layers to Reitman's delicately observed film and the flawed yet deeply sympathetic characters, who struggle to articulate their fears to each other and prefer to suffer in anguished silence.

It is not until a 21st century Mary Poppins, who takes multitasking to dizzying new heights, materialises in the fractured family home and re-energises the exhausted matriarch with an endless supply of self-help aphorisms, that an emotional dam breaks and the words and tears cascade.

Charlize Theron delivers a heartbreaking performance as a mother of three who is desperate to dodge the postnatal depression she suffered after the birth of her "quirky" second child, but is reluctant to ask for help.

It's a transformative role for the Oscar-winning actress, who gained more than 20kg to convincingly portray her cluckless mother hen.

Marlo (Theron) is poised to give birth and welcome a new life into the cluttered home she shares with her husband Drew (Ron Livingston), son Jonah (Asher Miles Fallica) and eight-year-old daughter Sarah (Lia Frankland).

Her wealthy brother Craig (Mark Duplass) is concerned that Marlo won't cope and he offers to pay for a night nanny, who will take care of the baby after dark, allowing his sister to get a good night's sleep.

Initially, Marlo rejects his kind offer and she soldiers on, trading barbs with concerned school headmistress Laurie (Gameela Wright), who fears her staff can't adequately cater to Jonah special needs.

When the pressure becomes too much, Marlo calls the night nanny and 26-year-old Tully (Mackenzie Davis) arrives at the front door and immediately takes charge.

"I'm like Saudi Arabia. I have an energy surplus," grins Tully as she bakes, cleans and nurtures while mere mortals sleep.

Marlo forges a close bond with the enigmatic younger woman, and that friendship deepens when it becomes evident that Tully's expertise extends far beyond mewling newborns.

"You can't be a good mother if you don't practise self-care," she counsels soothingly.

Tully is carefully embroidered with exquisite lines of pithy dialogue that demonstrate Cody's finely tuned ear for free-flowing conversation.

Theron is the picture's steady emotional heartbeat and her raw, unselfconscious portrayal nourishes supporting cast including a luminous turn from Davis.

The audacity of the final act will prove divisive but fortune favours the brave and Reitman's picture is quietly assured in its boldness. 8/10