Police headquarters in Oslo, Grønlandsleiret, number 44. An address with no historical resonance; not like 19 Møllergata, the old police headquarters, and very different from Victoria Terrasse, with its grand government buildings. Number 44 Grønlandsleiret had a dreary ring to it, grey and modern, with a hint of public service incompetence and internal wranglings. A huge and slightly curved building, as if the winds had been too strong to withstand, it stood framed by a house of God on one side and a prison on the other, with an area of demolished housing on Enerhaugen at the rear, and only a broad expanse of grass fronting it as protection against the city’s most polluted and trafficky streets. The entrance was cheerless and forbidding, rather small in proportion to the two-hundred-metre length of the façade, squashed in obliquely, almost concealed, as if to make approach difficult, and escape impossible.

At half past nine on Monday morning Karen Borg, a lawyer, came walking up the incline of the paved path to this doorway. The distance was just far enough to make your clothes feel clammy. She was sure the hill must have been constructed deliberately so that everyone would enter Oslo police headquarters in a slight sweat.

She pushed against the heavy metal doors and went into the foyer. If she’d had more time, she’d have noticed the invisible barrier across the floor. Norwegians bound for foreign shores were queueing for their red passports on the sunny side of the enormous room. On the north side, packed in beneath the gallery, were the dark-skinned people, apprehensive, hands damp with perspiration after hours of waiting to be told their fate in the Police Immigration Department.

But Karen Borg was late. She cast a glance up to the gallery round the walls: blue doors and linoleum floor on one side, and yellow on the other, southern, side. On the west side two tunnel-like corridors in red and green disappeared into nothingness.