Ross got out the card again. The vortex on its surface was twisting, reaching forwards, the map distorting more and more as they got closer. ‘Incredibly,’ she said.

The art gallery was open late for a new exhibition: Metaphysical: The Nostalgia of the Infinite. The poster had made Ross wonder if, despite the occult underworld’s problems with the whole concept of modernity, this might in fact be an exhibition that suited it. What she took from the accompanying leaflet: the concept of items or buildings being placed to overshadow and influence people – surely that struck a nerve with them? The Turbine Hall was packed with people queuing to get up to level three, where the exhibition was. Ross recalled seeing something about this having suddenly become one of those summer art ticket rushes London had, with staggered entry and sweaty groups of people craning to look at the paintings, even as the suburbs burned.

Thankfully, their destination was down in the Tanks, originally underground oil reservoirs, some of which were now used for exhibitions themselves, but not all. They saw more of the Sighted sort of people as they made their way through an installation where projectors would suddenly display random film clips of people talking about dead relatives. The Sighted they saw, in their ragged period costume, were sighing or walking quickly through or even sniggering at the exhibit. ‘It’s sort of like a half-hearted version of our lives now,’ said Costain, standing in the light of a woman sobbing uncontrollably, holding up a picture of what must have been her dead teenage son. ‘No wonder they don’t like it.’

‘I think maybe,’ said Ross, ‘they just don’t like modern art.’

She found the side door she had located a few days before, which had now been left unlocked, and followed a furtive-looking group of the Sighted through it.

There was nobody checking invites at the door. To know where the auction was seemed to be enough. The room they entered didn’t look as if it was part of the Tate – more as if it might still be a working part of a power station. Perhaps the pipes overhead did gleam a little too brightly, and the wall that seemed to be taken up with one big engine did so a touch artfully, but it was considerably more authentic than its surroundings. Right beside it, yes, Ross could feel it through the wall, they were up against the river here. It roiled and fretted just feet away.