And she then posed on the front steps for a lone photographer who had turned up with a disinterested-looking journalist who asked a series of lacklustre questions. It was two days before Slumberdown. No one shows much enthusiasm about anything in the last week before bedding down.

‘Come with me,’ said Logan once the mayor had departed, yawning, back to City Hall.

All Dormitoria were built to a standardised design, not refined much since initial adoption by Constantine in the fourth century. A circular building, usually capped by a steep conical roof, with twenty or more floors and a central thermal distribution shaft that ran up the centre. The stairs were either embedded in the stout and well-insulated walls, or, as here, wound their way in a spiral fashion up the central void.

Oliver Tiffen’s room was on the eighth floor and Logan used his Omnikey to gain access. The room was dimly lit, and of the standard pizza layout: a one-eighth slice of the circular floor, with the door at the truncated sharp end. The rest was divided into bathroom, bedroom and living area. Heat and light were valued commodities, but from opposite directions: heat from the central core that ran up through the building, light through triple-glazed slots in the outer wall.

We found Mrs Tiffen in the bedroom, surrounded by packing cases of food. She was well nourished, but utterly vacant – Oliver Tiffen had been harbouring his wife since she turned nightwalker. She clacked her teeth at us, then launched into a lively rendition of ‘Help Yourself’ on the bouzouki.

‘Plays it well, doesn’t she?’ said Logan.

It wasn’t unusual for nightwalkers to display skills dredged up from the tatters of their memory. Most knew a few words and could do a trick of some sort, even as mundane as finding their way to the shops or tuning a wireless. A very few, however, could do quite extraordinary things, like ice-skate and play Canasta. Mrs Tiffen was one of these, or, in the parlance of nightwalkers, ‘Tricksy’. Rumour had it the more advanced redeployed – the Edwards and Janes, for instance – were based on these individuals. More upstairs to rewire, apparently.

‘Your husband just drowned under twenty tons of boron slurry,’ said Logan to Mrs Tiffen, ‘but he fulfilled his duty without fuss or drama. If you could be proud of him, you would be.’

Mrs Tiffen didn’t react and just continued to play the bouzouki.

‘Why go to all this trouble keeping her?’ I asked as we stared at the woman, who seemed healthy enough, if a little pale in her demeanour. ‘And to volunteer yourself so young for High Octane and such a potentially gruesome death?’

In answer, Logan passed me the envelope Oliver Tiffen had given him before he went down into the HotPot chamber. The letter was not long.