The arrival of Steppenwolf of Chicago on the South Bank is a truly momentous occasion. Last seen here in 1989 with a knockout production of The Grapes of Wrath led by founder member Gary Sinise, their incendiary presentation of Tracy Letts’ big and blowsy, Tony-award winning Oklahoma family drama is a sensation: this is simply one of the greatest acting companies in the world and you have to see them.

As director Anna D Shapiro explained to Whatsonstage in this month’s magazine, “August” means the end of something, “Osage” is an indigenous people’s, or native American, term for where they live, and “County” stands for the colonial assignment by other people – Germans, Dutch, New Yorkers, whoever – who displaced them. All these strands exist in the layering of the play contained within a large three-storey house near Pawhuska, sixty miles west of Tulsa.

In the opening scene, the family patriarch Beverly (Chelcie Ross), a booze-sodden 1960s relic of a poet, is hiring a Cheyenne housekeeper Johnna (calm and beautiful Kimberly Guerrero) to the self-inflicted strains of T S Eliot. But in contrast to The Family Reunion, this show is less about the paw under the door than the fist in the face. Beverly’s about to check out big time, leaving his pill-popping wife Violet (scrawny, feisty, manipulative, evil, in Deanna Dunagan’s amazing performance) to shuffle and exploit the affections of their three middle-aged daughters.

The eldest, Barbara (the astonishing Amy Morton, a sort of wounded powerhouse amalgam of Penelope Wilton and Vanessa Redgrave) is a college librarian in Boulder, Colorado, where her teacher husband Bill (Steppenwolf founder member Jeff Perry) is having an affair with a student; their daughter Jean (Molly Ranson) is a pubescent (big boobs) pot-smoking wise child who befriends the isolated Johnna.

Second daughter Ivy (Sally Murphy) is a stay-at-home victim with an incestuous crush on her first cousin Charlie (Ian Barford) whose mother, Vi’s sister, is given the slam dunk steamroller works by the magnificent red-headed Rondi Reed. And third daughter Karen (Mariann Mayberry) breezes flakily in from Florida with her repellent fiancé, thrice-married Steve (Gary Cole) in tow.

The three-and-a-half hour play develops with the epic grandeur of Eugene O’Neill, the raw bitchiness of Edward Albee and as a study of social disintegration masquerading as a family gathering worthy of Alan Ayckbourn at his best. The chief point, though, is that Letts has written for fellow company members he knows well; this is bespoke material, and one of the greatest nights in the theatre I can recall.

-Michael Coveney