A Gate at the Stairs, By Lorrie Moore

Tassie Keltjin is the baby-faced babysitter from America's deepest Midwest who, by her own admission, is too green to have formed anything approximating a world view outside her father's potato farm - until life on the bland plains of Dellacrosse collides with a never-before-encountered urbanity in her university town of Troy.

It is still the Midwest but for the fresh-faced farm-girl, it is the "great unknown" outside the foetal comforts of the homestead. Her face reflects "the kind of smooth, round stupidity that did not prompt the world's study" when she meets her employer, Sarah Thornwood-Brink, a pin-thin sophisticate too busy running her restaurant to tend to her "biracial" adoptive daughter.

But if Tassie is puppy-faced, she is beguilingly so. The narrative voice of Lorrie Moore's third novel – and the first major offering after an 11-year hiatus - is simultaneously naive and knowing. Tessie might profess to be emotionally unformed but her voice is a magnificently mature stream-of-consciousness, which engulfs the reader with the wit, wisdom and occasional blasts of venom of a far older Tassie who is looking back - contemptuously at times - at her 20-year-old self.

The story is told under the absent shadow of the Twin Towers, blasted to embers just a year earlier, and while it is not a simple tale of the loss of innocence, Tassie - and the Midwest - can no longer seek refuge in the American dream, which is exposed to be as illusory as an episode of The Waltons.

Moore adds to Tassie's "round-faced innocence" a sense of mischief and tar black humour. For a country girl, Tassie grows to sound more like an urban rapper, a half-Jewish Slim Shady who plays bass, uses her room-mate's vibrator to stir her coffee and observes the "best'"of America with the gaze of a scornful outsider. "Indian buffet's 'all you can eat for a dollar'", she reflects in a shopping district, "but if you ate too much and stayed too long, they started showing you slides of their home village, which made you feel pretty awful".

With this blend of childlike clarity and adult wisdom, Moore unpicks Tassie's "potato country" where racism, terrorism and high consumerism lurks, barely disguised, at every parking lot and pizza parlour. In this ultra-ordinary America, the jihadi and the GI have become unsuspecting neighbours; Tassie's younger brother signs up with the army and finds himself instantly dispatched to Helmand, while her dark-skinned "South American" boyfriend turns out not to be who he seems (with a few giveaway clues such as his prayer mat and a predilection for "early morning curry which I then believed to be Brazilian cuisine").

Moore's vitriol is best reserved for the Thornwood-Brinks, whose adoption of Emmie, their part-African American baby, is laced with guilt. "So I didn't name her Maya or Kadire or Tywalla. I named her Emmie. Was that so wrong?" Sarah whines, with what sounds like Moore scoffing in the background. Sarah is a brilliant parody of the paranoid, time-starved modern mother. By day, she attends to the pressures of the "mill", her chi-chi eaterie where she has perfected the art of caramelising sage. By night, she collects self-flagellating liberals for boozy conflabs during which they berate themselves for the inequities of America's persecuted minorities.

While the nuts and bolts of motherhood must be delegated to Tassie, Sarah appears to take charge of the role, conceptually, at least. When she hears the latest song that Emmie has learnt from her babysitter, "I Been Working on the Railroad", there is every reason for moral panic. "There's just two things I'm worried about with that: the grammar and the use of slave labour". Are you serious, Tassie wonders later. Sarah is, of course, deadly serious. But for all its comic vivacity, the book reads like an elegy to the notion of an American pastoral, with a doom-laden storyline that rumbles with a locomotive energy towards disaster and the end of an innocence that never really was.

Moore's prose is full of the same stylistic puns and ribaldry of her short stories; but it also contains exquisite poetry which does not allow the reader to skim read or skit on the surface. It demands total absorption, with its verbal coils and spirals, and her wordplay, like Ali Smith's, sparkles with intelligence. A pearl necklace given to Tassie as a rite-of-passage by her mother is a "gyno-noose"; a lyrically-minded Muslim extremist is like "Gertrude Stein speaking from inside a burka". If forced to find fault, too many jokes get in the way of Moore's word-smithery, jostling for laughs when the reader would be satisfied just to marvel at her sentences which, one imagines, were lovingly hewn, carved and polished, over Moore's 11 years of poetic silence, emerging now like a thing of beauty.