Oslo is not a city whose streets hum with urban tension and social decay. To the casual observer, the Norwegian capital is a study in frictionless living: clean, well-ordered, civic-minded, affluent yet essentially egalitarian in spirit. There are more paintings by Edvard Munch here than there are graffiti, and Saturday night in town can seem about as frenetic as a bank holiday in Sunningdale. The locals speak with metropolitan pride about the edginess of the “east side”, where most of the city’s non-European immigrants live, but from a British perspective even that neighbourhood seems like a model of residential tranquillity. Yet these placid streets have produced countless psychopaths, serial killers, political assassins and degenerates of every conceivable stripe.