(The numerals came from an exchange between the mathematicians G. H. Hardy and S. I. Ramanujan in 1920, when Hardy went in a taxi cab with that number to visit his dying colleague in hospital and complained it was ‘a rather dull number’, to which Ramanujan responded: ‘No, Hardy! No, Hardy! It is a very interesting number. It is the smallest number expressible as the sum of two cubes in two different ways.’) He left just one lamp lit downstairs – of that he was sure – then climbed the curved white marble staircase to the bathroom. He took off his spectacles, undressed, washed, brushed his teeth and put on a pair of blue silk pyjamas. He set the alarm on his mobile for six thirty, registering as he did so that the time was then twenty past twelve.

In the bedroom he was surprised to find Gabrielle still awake, lying on her back on the counterpane in a black silk kimono. A scented candle flickered on the dressing table; otherwise the room was in darkness. Her hands were clasped behind her head, her elbows sharply pointed away from her, her legs crossed at the knee. One slim white foot, the toenails painted dark red, was making impatient circles in the fragrant air.

‘Oh God,’ he said. ‘I’d forgotten the date.’

‘Don’t worry.’ She untied her belt and parted the silk, then held out her arms to him. ‘I never forget it.’

IT MUST HAVE been about three fifty in the morning that something caused Hoffmann to wake. He struggled up from the depths of sleep and opened his eyes to behold a celestial vision of fiery white light. It was geometrically formed, like a graph, with thinly spaced horizontal lines and wide-apart vertical columns, but with no data plotted – a mathematician’s dream, but not in fact a dream, he realised after squinting at it for a few seconds; rather the result of eight five-hundred-watt tungsten-halogen security lights shining brilliantly through the slats of the window blinds – enough wattage to light a small soccer ground; he had been meaning to have them changed.