Rivers put the car into reverse, and the tractor treads crunched across the stone floor as he guided it carefully between the close-packed hovels and sleeping bodies, veering close enough to outstretched limbs at times to send Dakota’s heart leaping towards her mouth. She studied the weapon’s components and then carefully slotted them together, the grip sliding in last. When she held it in her upturned palm it felt light, insubstantial, more like a toy than a real weapon. Hugh Moss would have access to far greater firepower than this.

‘I don’t mean to pry,’ said Rivers, ‘but you said at one point you thought you might have trouble finding your way around on your own . . . ?’

‘I can’t manipulate data the way I used to, Mr Rivers. I’m not much more than a passenger on the Magi ships these days.’

Rivers nodded, looking embarrassed. ‘I’m sorry for asking. It seems so many of us are suffering from the bends.’

She frowned. ‘The what?’

‘That’s what some of the other navigators are calling it now,’ Rivers explained. ‘The bends, or neural burnout – a sickness from diving too deep into the world of data contained inside every Magi ship.’

‘Really.’

‘I’ve not been affected myself,’ Rivers continued. ‘But I suspect it may only be a matter of time.’

‘How long have you been a Magi-class navigator?’

‘Six months,’ he replied. ‘Most navigators start suffering the ill effects after seven or eight months.’ His smile faded a little. ‘We should be going now. I found you a place to stay on a lower level.’

Before long they were trundling through a series of endlessly winding passageways. Steps were carved into the stone on either side, every thirty metres or so, leading up to open galleries cut into the side of the passageways, just below the ceiling. Terran flora was everywhere, although much of it had clearly been engineered specially for an underground existence. Vines dropped down from the ceiling to brush against their heads as they drove on, while dwarf trees – oak, ash and a few unidentifiable hybrids – lined every district they passed through. These trees barely came up to shoulder height, and made Dakota feel like she and Rivers were a pair of giants going out for a Sunday drive.

Business districts merged into residential areas, the ceiling sometimes dipping so low that Dakota would have had to stoop if she disembarked, while at other times it soared to cathedral proportions, with tiers of recessed homes and businesses rising up and up, all interconnected by carved stone staircases. They moved through a cornucopia of odours, those of food cooked on open griddles in busy market places, the fragrance of pale-leaved flowers and the rankness of thousands of human bodies living for years at a time in this deep subterranean darkness. And as they moved from one district via a downwards-spiralling ramp to a lower district, the air became ever hotter, denser and damper.