Rating: R Grade: B+

Once again, playwright Tracy Letts (“Killer Joe” in conjunction with director William Friedkin and the resurgent Matthew McConaughey as the titular killer subject) adapts his own award-winning stage piece – which I caught during its packed press screening at the Toronto International Film Festival – with John Wells, producer and writer of television shows like “ER” and “The West Wing” before jumping to the big screen with “The Company Men,” helming for a feature for just the second time, and there’s another predator on the loose in Letts-land.

Violet Weston (Meryl Streep) is an animalistic force of nature, a marauding mauler of a mother. It is surprising any of her offspring even survived those first days outside her womb. Violet seems like she would have swallowed them whole before the umbilical cord could be cut; they would have been nothing more than sustenance for her uncontrollable hunger. Likely, what saved those poor newborns was their father Beverly (Sam Shepard). We see him early on, prepping Johnna (Misty Upham), a Native American home care aid, for the task of holding her own against Violet and we recognize a patience in Beverly, a quiet gentleness that should not be mistaken for anything other than steely resolve. He has been able to fend off the poisonous advances – without a doubt, daily attacks – from Violet for years, but the effort has taken its toll on him. He looks like a Japanese warrior engaged in the ritual exercise of his honorable suicide.

So, when he first goes missing, and then is confirmed dead, it falls to his children and extended family to carry on, to maintain what honor he has been able to preserve for them. But what a tarnished burden it is for each of them. Eldest daughter Barbara (Julia Roberts) drags along a teen daughter (Abigail Breslin) of her own and a husband (Ewan McGregor), in the midst of leaving her for another woman. Baby girl Karen (Juliette Lewis) waltzes in with her latest older man (Dermot Mulroney), a slickster ill-prepared for the savagery he will encounter. While middle daughter Ivy (Julianne Nicholson), the one child who has remained close by, longs for freedom and bears a secret happiness that cannot survive the harsh reality of mid-Weston life. Violet’s sister Mattie Fae (Margo Martindale), her rambling-shambling husband Charlie (Chris Cooper) and their son Little Charles (Benedict Cumberbatch) round out the hapless clan.

“August: Osage County” exists not merely as a time or place apart from what we might imagine of family dysfunction; the tale of the Westons aspires to the epic failed humanity of the Greek gods. The exchanges advance beyond capital “D” drama to the screaming hype of full caps followed by a long line of exclamation points for emphasis. It goes without saying that to bring this to life, you need a one-of-a-kind presence to seize the weight of it all and hoist it upon her back.

That would be Streep. Her Violet is a figure above and beyond the tragic. Streep pops tragedy like the pills she consumes during the course of the day. They do nothing for her, but she refuses to live without them. Rather than sugary sweetness, Violet can’t get enough of the bitterness of the pills and tragedy life has thrown her way. Streep taps into this and uses it to excuse the hunger that leads her to devour everything – scenery and performers – in her wake.

Which, oddly, speaks volumes for Roberts, because as Barbara she is the only actor in this talented bunch who slips free of Streep’s tight jaws. Roberts proves perfect for a filmed adaptation opposite Streep, thanks to those moments when Wells draws us up close and personal next to Barbara so we can see the irresistible force she has obviously inherited from Violet. I never thought I would dream of Roberts as an heir of Streep’s, but she’s a survivor.