Every day was like the first day of their lives, and a vivid delight.

Malenfant wondered how it was possible for such people as these — intelligent, complex, vibrant — to have become extinct.

Extinct: a brutal, uncompromising word. Extinction made death even more of a hard cold wall, because it was the death of the species. It no longer mattered, truthfully, how sophisticated the Neandertals’ sign language had been, whether they had been capable of true humanlike speech, how rich was their deep-embedded consciousness. Because it was all gone.

The Neandertals had been brought back for this short Indian summer to serve the Gaijin’s purposes. But this had not cheated the extinction, because these Neandertals were not those who had gone before; they had no memory of their forebears, no continuity. The extinction of the Neandertals, in the deep past of Earth, had buried hope and memory, disconnected the past from the future.

And now, Malenfant feared, the time was drawing close for an extinction event on a still more massive scale: extinction across multiple star systems, so complete that not even bones and tools would be left behind for some future archaeologist to ponder.

Valentina woke him with a kick. She beckoned him, a universal gesture, and handed him his suit.

He got dressed groggily and followed her out of the teepee.

Out on the surface, he relieved himself and looked around. Io was in eclipse right now, so that the pinpoint Sun was hidden by Jupiter. The ground was darkened by the giant planet’s shadow, illumined only by starlight and by an auroral glow from Jupiter, which was otherwise a hole in the sky.

As the warm fluid trickled uncomfortably down his leg, he stumbled after Valentina, who had already set off across the crusty plain.

There were five Neandertals in the party, plus Malenfant. They were all carrying bags of tools. The Neandertals moved at a loping half-jog that Malenfant found almost impossible to match, despite the gravity.

They kept this up for an hour, maybe more. Then they stopped, abruptly. Malenfant leaned forward and propped himself up against his knees, wheezing.

There was something here. A line on the ground, shining silver in the starlight. It arrowed straight for the swollen face of Jupiter.

Malenfant recognized the texture. It was the same material he’d seen trailing from the roots of Trees, in orbit: material that had been found on the surface of Venus.

It was superconductor cable.

The Neandertals, signing busily, pressed a gadget to the cable. Malenfant couldn’t see what they were doing. Maybe this was some kind of diagnostic tool. After a couple of minutes, they straightened up and moved on.

As they trotted, the eclipse was finishing. The Sun started to poke out from behind Jupiter’s limb, a shrunken disc that rose up through layers of cloud; orange-yellow light fled through the churning cloud decks, casting shadows longer than Earth’s diameter.

The dawn light caught Io’s flux tube. It was like a vast, wispy tornado reaching up over his head. The flux tube was a misty flow of charged particles hurled up from Io’s endless volcanoes’ sweeping in elegant magnetic-field curves into the face of the giant planet. And where the tube hit Jupiter’s upper atmosphere, hundreds of kilometers above the planet’s cloud decks, there was a continuing explosion: gases made hotter than the surface of the Sun, dragged across the face of the giant planet at orbital speed, patches of rippling aurora hundreds of kilometers across.

Io, a planet-sized body shoving its way through Jupiter’s magnetosphere, was like a giant electrical generator. There was a potential difference of hundreds of thousands of volts across the moon’s diameter, currents of millions of amps flowing through the ionosphere.

Standing here, peering up into the flux tube itself, the physical sense of energy was immense; Malenfant wanted to quail, to protect himself from the sleet of high-energy particles that must be gushing down from the sky. But he stood straight, facing this godlike play of energy. Not in front of the Neandertals, he told himself.

Soon they arrived at a place where the cable was buried by a flow of sulphurous lava, now frozen solid. After a flurry of signs, the Neandertals unpacked simple shovels and picks and began to hack away at the lava, exposing the cable.

Malenfant longed to rest. His legs seized up in agonizing cramps; the muscles felt like boulders. But, he felt, he had to earn his corn. He rubbed his legs and joined the others. He used a pick on the lava, and helped haul away the debris.

He couldn’t believe this was the only length of superconductor on Io. He imagined the whole damn moon being swathed by a net of the stuff, wrapping the shifting surface like lines of longitude. Perhaps it had been mined from Venus, scavenged from that ancient, failed project, brought here for some new purpose of the Gaijin.

The Neandertals’ job must be to maintain the superconductor network, to dig it out. Otherwise, such was the resurfacing rate on this ferocious little moon, the net would surely be buried in a couple of centuries or so. The work would be haphazard, as the Neandertals could travel only where the volcanic hot spots allowed them. But, given enough time, they could cover the whole moon.

It was a smart arrangement, he thought. It gave the Neandertals a world of their own, safe from the predations of Homo Sap. And it gave the builders of this net — presumably the Gaijin — a cheap and reliable source of maintenance labor.

Neandertals were patient, and dogged. On Earth, they had persisted with a technology that suited them, all but unchanged, for sixty thousand years. They might already have been here, on Io, for centuries. With Neandertals, the Gaijin had gotten a labor pool as smart as humans, not likely to breed themselves over their resource limits here, and lacking any of the angst and hassle that came with your typical Homo Sap workforce.

Smart deal, for the Gaijin.

All he had to do now was figure out the purpose of the net itself: this immense Gaijin project, evidently intent on tapping the huge natural energy flows of Io. What were they making here?

Without a word to Malenfant the Neandertals jogged off again, along the cable toward Jupiter.

Malenfant, wheezing, followed.

When they got back to the teepee, they found Esau had died.

Valentina was inordinately distressed. She hunkered down in a corner of the tent, her huge body heaving with sobs. Evidently she had had some close relation to Esau; perhaps he was her father, or brother.

Nobody seemed moved to comfort her.

Malenfant squatted down opposite her. He cupped her chinless jaw in his hand, and tried to raise up her huge head.

At first Valentina stayed hunched over. Then — hesitantly, clumsily, without looking at him — she lifted her huge hand and stroked the back of his head.

She looked up in surprise. Her hard, strong fingers had found a bony protrusion. It was called an occipital bun, Malenfant knew, a relic of his distant French ancestry. She grabbed his hand and pulled it to the back of her own scalp. There was a similar knotty bulge there, under her long black hair. Here was one place, anyhow, where they were similar. Maybe his own occipital bun was some relic of Neandertal ancestry, a ghost trace of some interspecies romance buried millennia in the past.

Valentina’s human eyes, buried under that ridge of bone, stared out at him with renewed curiosity. Her breasts were flat, her waist solid, her build as bulky as a man’s. And her face thrust forward with its great projecting nose, her puffed-up cheekbones, her long chinless jaw. But she wasn’t ugly to him. She was even beautiful.