Do you suffer from freckles?'' asks the ad. Pippi Longstocking marches right in and tells the shop lady "No." "But my dear child," responds that fount of rectitude, "your whole face is covered with them." "I know it," says Longstocking. "But I don't suffer from them. I love them. Good morning."

Like half of humanity I spent Christmas tied hand and foot, as it were, to Stieg Larsson's trilogy. And I can tell you this. Lisbeth Salander's dysfunctionality may knock Pippi's into a cocked hat but this tiny, tattooed curmudgeon of a hero is Larsson's Longstocking. She's his take on how Sweden's child-anarchist-of-choice would deal with a modern, adult world.

And boy, does she deal. In one astonishing sequence - astonishing because it works - the elfin Salander is surprised at a deserted cabin by two hired assassins programmed to "tear her apart and stuff her in their saddlebags". Within minutes she has hobbled one, sent 50,000 volts through the other's testicles and roared off on his Harley-Davidson with (the final indignity) his treasured bike club insignia padding her helmet. Another especially satisfying scene has Salander tattoo her vengeance - I am a sadistic pig, a pervert and a rapist - across the bourgeois belly of her tormenter.

This stuff makes Swedish critics grizzle. "Larsson's books depict a dark and violent Sweden, brimming with state and family secrets." But to non-Swedish tastebuds, the trilogy's dominant flavour - against which Salander makes stark counterpoint - is a low-church Ikea blond; prose so unvarnished, values so lofty and characters so cartoon-simple as to imbue an oaten plainness, more Amish than Witness.

How, then, did this high moral tale, swiftly plotted but clunky and arrhythmic in its prose, get so big? How did this uber-simplistic feminist diatribe from a socialist militant (whose only written will was a 30-year-old document leaving everything to the Umea Communist Workers League) become a world best seller?