You used to know where you stood with literary stereotypes. The Russians did agony; the French, ecstasy; the Americans, naivety. And the British? Ah, the British did irony. How things change. A bestselling American author - OK, he does live here - publishes a memoir just bulging with droll narrative swerves, shimmies and double-takes that at the same time overegg and undercut his subject and himself. The result is a sophisticated book about simplicity, and a knowing account of ignorance. So what happens to it in the alleged capital of the sarky and the snide? The volume arrives to a literal-minded chorus of patronising praise that utterly fails to register the chill beneath its charm. I think we must be suffering from a surfeit of mind-rotting Betjemania.
Not that anyone would ever want to confuse Bill Bryson with Jonathan Swift. No doubt our favourite comic travel writer really did adore as much about his 1950s childhood in Des Moines, Iowa, as his memories suggest in The Life and Times of the Thunderbolt Kid (Doubleday, £18.99). I'm sure that in the safe, prosperous heartland of the post-war superpower, the NeHi grape pop did let Billy the baseball writer's son see "to the edge of the universe"; and that the Toddle House in Des Moines served the world's "smoothest, most mouth-pleasing banana cream pie". Whether browsing the superhero comics at Kiddies Coral, visiting the Tea Room at Younkers department store ("a state room from Buckingham Palace magically transported to the Middle West") or wolfing meatloaves "the size of a V8 engine" at potluck suppers with his grandparents, Bryson captures the wide-eyed glee of a baby-boom boyhood with the relish you'd expect. So does this feel like paradise amid the cornfields? No - more like a spooky out-take from The Truman Show.
That knack of standing inside and outside the Middle-American dream makes his memoir much smarter, and stranger, than its billing as a gentle glut of nostalgia. Bryson loves the performance, but he also turns a spotlight behind the scenes to expose the technicians in the wings - the wizards who direct this Oz. Nuclear anxieties shadow the decade from the first H-bomb explosion in 1952 to the Cuban Missile Crisis. Hysterical anti-Communism makes it "an especially wonderful time to be a noisy moron". Bryson opens the doors of the theatre of plenty to show us black men executed for stealing a dollar, CIA-backed massacres in Guatemala, real-life Strangeloves perfecting their "gigantically ferocious" bombs.
This is a wittily incisive book about innocence, and its limits, but in no sense an innocent book. (Was their bourbon-sipping family physician actually called Dr Alzheimer?) For the Brysons, as for this blessed plot of affluent America, "No one ever got lastingly hurt... Nothing ever went seriously wrong." Land, money, arms and the "big buffering oceans" shield them. A presiding fantasy of omnipotence climaxes in Billy's self-appointed role as the Thunderbolt Kid, the cosmic warrior able instantly to zap every pesky enemy into "a small hard carbonised lump".
Like Alan Bennett, another ironist posing as a sentimentalist, Bryson can play the teddy-bear and then deliver a sudden, grizzly-style swipe. Which doesn't make his book any less engaging a slice of baby-boomer heaven than its hype now pretends. Yet asperity vies with affection. While other superheroes of the time battled Commie agents, the Thunderbolt Kid had a more specific target in his sights: "I killed morons. Still do."
Our bookshelves now heave with volumes that offer to explain US "exceptionalism". None of the experts responsible for them is likely to propose that a string of amusing yarns about Des Moines might tell us as much about the oddities of the American way as a dozen think-tanks. So I will.