When a frazzled mom-of-five sallies forth into the garden to deliver an excruciating accappella rendition of Climb Every Mountain she's doing it because she "always wanted to be a Von Trapp - a credit to Austria."
Unfortunately, she's not a member of the famous singing troupe but put-upon housewife Shirley Moochmore (Gibney). And she's not in Salzburg but the smalltown Australia of Dolphin Heads.
She's also going mad. And so are her five children, who have diagnosed themselves with psychological maladies ranging from schizophrenia to bipolarity.
Following one particularly wacko episode when she fantasises that her philandering local politician husband Barry (LaPaglia) has won Wheel of Fortune, she goes on a massive spending spree...and he gets her taken off to the funny farm.
With no-one left to look after the girls, Barry impulsively gives the gig to hitchhiker Shaz (Collette), a knife-wielding bohemian whose off-kilter view of the world - and acid distaste for suburban conformity - gradually appeals to her new charges.
First of all, there's scores to be settled - with the draconian snob next door who cleans her driveway with a toothbrush and the coffee shop bitch-from-hell, a sly sadist who's made the nervy Shirley's life a misery.
These dealt with in her colourful way, Shaz's attentions turn to the promiscuous Barry... but she's got her own demons to deal with in the form of shark hunter Trevor (Schreiber), the employer of the eldest Moochmore waif Coral.
It's been almost 20 years since director PJ Hogan's raucous Muriel's Wedding (also starring Collette) and this splendidly enjoyable comedy channels a hefty dollop of that movie's spunky joie de vivre.
Hogan demonstrates a sure ear for droll dialogue and his script - while occasionally too broad for some audiences - is delivered with delirious panache by his up-for-it cast.
Unthinking convention gets a sound kicking and it's nice to get a lesson in empowerment that's not delivered in a middle management powerpoint presentation.
You'd be mad to miss it.