When intelligence evolved among Swimmer’s predecessors, their biology shaped everything they did. Unlike humans their politics was a matter of cooperation rather than competition, though there could be disagreements, even wars. They crawled out onto land - surely the low gravity helped them with that conquest - where there were raw materials to be shaped, power sources like fire impossible under water. Their different origins shaped their technology. They discovered a genius for moulding themselves and their coevals; these people were capable of advanced biochemistry, though their physical technology was no more than Iron Age.

They had even managed to achieve spaceflight. A handful of Swimmer’s people cloaked themselves in a new kind of hide, a tough, silvered skin capable of retaining inner heat while resisting the harsh radiations of space. In time ice moons and comet nuclei had become home to a new variant of Swimmer’s kind, who rarely visited the home planet.

But all the while the pulsar continued its slow, lethal work of slicing away the substance of the sun.

As this story unfolded, the Spear crew exchanged glances of recognition.

It had become increasingly clear that a crisis was approaching. A decision emerged from the interconnected councils of the people. The interplanetary wayfarers were summoned home. The most technologically advanced of their kind, perhaps they could find a way to save the world.

The space-hardened wayfarers returned. By now the ice cap on the nightside, hard and cold, was not so different a habitat from the ice moons they had made their home. But they found they resented being begged for help by those they regarded as a primitive, weaker form. They saw ways to use this fat rocky world for their own purposes - and all the better if the murky atmosphere and muddy oceans were frozen or stripped off.

Bringing the spaceborne home was a catastrophic mistake. They had diverged too much from Swimmer’s kind. There were two species now, too far apart, competing for the same space. Conflict was inevitable.

The nightsiders were outnumbered by the daysiders, but were far more technologically advanced. For centuries they had been launching missile after missile over the terminator, from the dark to the light. At first the daysiders had fought back; epic invasions of the night had been launched. But as its cities and farms were devastated, the thin material base of the dayside crumbled. By now only scattered survivors, like Swimmer, remained. They mounted guerrilla actions against nightside patrols. But they knew the war was lost, and their future with it.

And recently, as if they had not suffered enough, a new peril had arisen, when a new light crossed the sky.

‘The habitat of the Black Ghost,’ Borno said grimly.