‘Who built it?’ he said, as if she had asked him. He shrugged. ‘How would I know? Lizard People from deep time. They were all over the Halo for a while, you find traces of them even on a dump like Panamax IV.’

The assistant shivered.

As soon as they left the surface she had felt her tailoring come up. Now she looked back along the passage, which just there was full of brown light and had an old monorail running along it.

‘Something’s in here with us,’ she said.

‘People often think that.’ The labyrinth, Gaines said, was a perfect venue for standing acoustic waves: at around nineteen Hertz these would commonly generate feelings of dread, bouts of panic, visual defects and hallucinations. ‘Down at twelve you just vomit endlessly.’

Half a mile along, the architecture changed suddenly and they were in primitive, squared-off passageways driven through basalt. When the boys from Earth arrived, there had been no light here worth speaking of for a hundred millennia. ‘We call it the PCM,’ Gaines said. ‘Pearlant Cultural Minimum. Suddenly you can see the tool marks. These sections may be the oldest of all, tunnelled into the rocky material before it aggregated, when it was part of something else. Or maybe their civilisation just lost traction on things for a while. Or these areas might have had a religious purpose. There’s no physics worth speaking of down here, but we get panel art. Look.’ He stopped in front of what appeared to be a section of bas reliefs, which showed three modified diapsids wearing complex ritual clothing. One of them was strangling a fourth, who lay passively on what looked like a stone bier.

‘These people were a million years ahead of us, but they were still trying to work out how to be rational. I don’t think they ever quite made it. The Aleph was only one of their projects.’

He took her arm again.‘Are you ready? It’s through that next door.’

On Saudade, Epstein the thin cop got a call to go to one of the bonded warehouses at the noncorporate rocket port. It was 4.20 am. Exactly two minutes earlier, the corpse of Enka Mercury had vanished. Edits of the nanocam coverage showed a translucent, fish-coloured image of Enka – through which you could make out the ribbed alloy walls of the warehouse – suddenly replaced by nothing. No matter how many cuts the operator made, there was no transition phase. One minute Enka was clinging on – her expression, when you could see it, as determined as it had been from the start, the expression of someone who had died but had never given up – the next, she was gone.