‘So then it turns and heads for the Peerless?’ Tarquinia suggested. ‘The rogue’s instructors are planning to announce that a gnat loaded with antimatter is on its way – but they’ve offset it far enough from the Station that they think we’ll have no idea where to look for it.’

‘That’s a possibility,’ Greta replied. ‘But they might not be trying to bargain at all. Why enter into negotiations if they can get what they want directly?’

Ramiro felt sick. ‘You think they’ll try to destroy the engines, without warning?’ Crashing a gnat into the base of the mountain – with either enough antimatter or enough sheer kinetic energy to do the job – would probably kill half the population in the process.

Greta’s voice crackled.

‘Say again,’ Tarquinia requested.

‘Not the engines. The corridor.’

Ramiro struggled to hear what followed, but eventually Greta’s theory became clear. She believed the rogue was doing nothing more than giving itself a run-up: travelling away from the Station in order to turn around and come back – with as much velocity as possible. Its target wasn’t the Peerless. It was the Station.

Given the angle of arrival, the collision would set the Station on a grazing trajectory towards the Object. When all those empty workshops and living quarters skidded across the surface of the asteroid, the explosion would send a plume of antimatter far out into the void – and the geometry of the impact would guarantee that the plume polluted a region that the Peerless needed to traverse if it was to commence the turnaround.

The hazard would take a generation to disperse. If they tried to steer the mountain through the debris, the system that protected the slopes from the usual smattering of tiny specks of antimatter would be utterly overwhelmed – and the failures would not be embarrassing spot fires, they’d be blasts that tore cavernous holes in the mountainside and risked setting everything ablaze.

‘Can we move the Station?’ Ramiro asked. The habitat’s own engines were weak things, intended to do no more than stabilise it in orbit around the Object, but if the rogue gnat could shift it with a few bells’ worth of accumulated power, surely their own benign craft could spend the same time gently towing it out of harm’s way?

‘Not quickly enough,’ Tarquinia replied. ‘With a load as massive as that, the limiting factor’s not our engines, it’s the strength of the tow ropes.’

‘Right.’ Ramiro had been wondering why the rogue wasn’t simply dragging the Station to its demise, but apart from the question of which approach would be the easiest to automate, the least conspicuous and the hardest to prevent, the go-away-come-back-and-crash method would actually deliver a faster result.

Greta said, ‘The only choice is to intercept the rogue.’

‘You couldn’t have worked all this out before we left?’ Ramiro complained. If the rogue came straight back towards the Station, there’d be nothing more to learn from its navigation system. They should have just tried to destroy it from the start.