Or, unexpectedly, during the day as they walked or rested, as something — the slither of a reptile, the chirp of an insect, the way the sunlight fell on a leaf — reminded her unaccountably of him.

She knew was grieving. She had seen it in others; she knew the symptoms. It wasn’t so much that she was managing to function despite her grief; rather, she thought, this unlikely project to go challenge Homo superior was something to occupy the surface of her mind, while the darker currents mixed and merged beneath. Therapy, self-prescribed.

The Hams seemed to understand grief. So they should, she thought bleakly; their lives were harder than any human’s she had known, brief lives immersed in loss and pain. But they did not try to soothe her or, God forbid, cheer her up.

There is no consolation, they seemed to be telling her. The Hams had no illusion of afterlife or redemption or hope. It was as if they were vastly mature, ancient, calm, compared to self-deluding mayfly humans, and they seemed to give her something of their great stolid strength.

And so she endured, day by day, step by step, approaching the base of that snake of twisting air.

It didn’t surprise Emma at all when the Hams, with the accuracy of expert map readers, walked out of the desert and straight into an inhabited community.

It was a system of caves, carved in what looked like limestone, in the eroded rim wall of what appeared to be a broad crater. The upper slopes were coated thinly by tough grass or heather, but the sheltered lower valleys were wooded. And the crater was at the very bottom of that huge captive twister, which howled continually, as if seeking to be free.

As she approached she made out the bulky forms of Hams, wrapped in their typical skin sheets, coming and going from scattered cave mouths that spread high up the hillsides.

Emma could see the advantages of the site. The cave mouths were mostly north facing, which would maximize the sunlight they captured and shelter them from the prevailing winds. She suspected the elevated position of the caves was a plus too. Maybe the migration paths of herd animals came this way. Hams preferred not to have to go too far to find their food; sitting in their caves, gazing out over the broken landscape around the crater, all they would have to do was wait for their food supply to come their way.

…But that wind snake curled into the air above their heads, strange, inexplicable, filling the air with its noise — even if it didn’t disturb so much as a dust grain. You’d think it would bother the Hams. She saw no sign that it did.

Emma and her companions walked to the foot of the crater wall, and began to clamber up. The adults glanced down at their approach, but turned away, incurious.

The first person who showed any interest in them was a child: stark naked, a greasy bundle of muscle and fat no more than three years old, with one finger lodged in his cavernous nostril. This little boy stared relentlessly at Emma and followed her, but at a safe distance of a yard or so; if she tried to get closer he backed away rapidly until his buffer of safety was restored. Ham children were much more like human children than their adult counterparts. But Ham kids grew fast; soon they lost the open wonder of youth, and settled into the comfortable, stultifying conservatism of adulthood.

She stepped into the mouth of the largest cave. The noise of the whirlwind was diminished. The sun was bright behind them, and Emma, dazzled, peered into the gloom.

The walls were softened and eroded, as if streaked with butter. There was a powerful stink of meat, coming from haunches and skins stacked at the back of the cave. The place was not designed for the convenience of people, she saw; the roof was so low in places that the Hams had to duck to pass, and crude lumps of rock stuck out awkwardly from the walls and floor. She recognized the usual pattern of Ham occupation: a floor strewn thick with trampled-down debris, an irregular patchwork of hearths. The roof was coated with soot from innumerable fires, and the walls at head height and below were worn away and blackened by the touch of bodies, generation on generation of them. This place had been lived in a long time.

Emma found a piece of wall that seemed unoccupied. She dumped her pack and sat down in the dirt.

A woman approached the travellers. Bent, her hair streaked with white, a tracery of scars covering her bare arms, she looked around eighty, but was probably no older than thirty-five or forty. She began to jabber in a guttural language Emma did not understand, with no discernible traces of English or any other human language. Julia seemed uncertain how to reply, but Mary and Joshua answered confidently. Neither party seemed ill at ease or even surprised to see the other.

Julia came to Emma.

Emma said, “So can we stay?”

Julia nodded, a Homo sap gesture Emma knew she affected for her benefit. “Stay.”

With relief Emma leaned back against the creamy, cool wall of the cave. She opened her pack and dug out her parachute silk blanket and a bundle of underwear to use as a pillow. The ground here, just crimson dust, much trodden and no doubt stuffed with the bones of Ham grandmothers, was soft by comparison with what she had become used to; soon she felt herself sliding towards sleep.

But she could hear the howl of that tame whirlwind, relentless, unnatural, profoundly disturbing.

She spent a full day doing nothing but letting her body recover, her head become used to the sights and sounds and smells of this new place.

Right outside the cave entrance, a stream of clear water worked its way through rocky crevices towards the impact-broken plain below. Its course was heavily eroded, so that it cascaded between lichen-crusted, round-bottomed pools. The people used the pools for washing and preparing food, though they drank from the higher, cleaner streams.

Emma waited until she wasn’t in anybody’s way. Then she drank her fill of the stream, and washed out her underwear, and spread it out to dry over the sunlit rocks.

As she tended her blistered feet and ulcerated legs, and made small repairs to her boots and underwear, she watched the hominids around her.

Her Ham companions seemed to settle in quickly, according to their nature. Mary, strong and powerful, spent happy hours wrestling with the younger men, besting them more often than not. By the end of the day she was hardening spear points in a hearth, apparently preparing for a hunt.

Julia seemed to make friends with a group of women and children who spent much of their time clustered around one hearth — she blended in so well, in fact, that Emma soon had trouble distinguishing her from her companions, as if she had been here all her life.

Joshua, a loner in his own community, was a loner here. He settled into a small, solitary cave, and Emma saw little of him. But the Hams here seemed to tolerate his eccentricities, as had his own people.

As for Emma, she was largely ignored, much as she been with her other communities of Hams. Unable to shake off a feeling of sufferance — after all, how would a Neandertal stray be treated if she wandered into a human community? — she did her best to keep out of everybody’s way.

There was one old man who seemed to take a liking to her, however — old, meaning maybe ten years younger than she was. He was badly disfigured by a swathe of scar tissue that lapped up from where his right ear should have been to the crown of his head. She didn’t have a word in common with this guy, and she couldn’t ask him about his injury. But this wounded, smiling man seemed vaguely curious about her: curious enough, anyhow, to offer her meat. The meat was a prime cut, apparently from the shoulder of some animal — an antelope, maybe, but it could have been a rhino for all she knew. It was a groaning bloody slab two fingers thick and twice the size of a dinner plate. Her benefactor watched with absent interest as she rigged up a frame of sticks to cook it over the nearest fire.