The bull tossed him, and the hunter swiveled around in midair, so that when he landed astride the animal’s back, he faced forward. It wasn’t a crotch-crushing impact—the man’s feet landed first, and his legs slid downward, already gripping so that when the man’s crotch came in contact with the bony ridge of the bull’s spine, his downward momentum was almost nil.

It was the most perfectly controlled athletic move Noxon had ever seen.

At the exact moment that the lead hunter was perfectly astride the aurochs, the three other hunters jabbed at one shoulder and both rear thighs, striking deeply enough that they did not try to withdraw the spears. The wounds would not be fatal in themselves, but because they left their spears in place, Noxon could imagine that if the lead hunter failed to bring down the beast, it would leave a trail of blood as it ran away, and would become weaker and weaker, so the hunters would be sure of a kill even if it wasn’t a quick one.

But the lead hunter was no novice. As he settled onto the bull’s back, his hands were already pulling the spear upward out of its binding. As the bull began to react to the wounds inflicted by the other hunters, the rider jabbed downward with enormous power, and the spear seemed to go twenty centimeters into the animal’s spine.

It shuddered once and then flopped sideways, having lost all control of its muscles when its spinal cord was severed.

As it fell, the lead hunter sprang from its back, so he was not pinned under it.

Noxon thought back through what the man had done. In a single fluid motion, he had caught the bull’s horns, vaulted into the air, spun halfway around, landed on his feet, slid down into a tight-gripping straddle, withdrawing his spear and stabbing in the exact place with all his strength and leverage, and then leapt clear of the animal. In realtime it hadn’t been as rapid as it seemed in slicetime, but Noxon hadn’t been slicing that fast. It really had been unbelievably quick.

The other three hunters fell on the fallen animal instantly, using small stone blades to slice open the throat and belly. They disemboweled the animal and skinned it in smooth, practiced movements, each man knowing and doing his job. Noxon sped up his time-slicing enough that they could see the whole process before they needed to leave. When the men had the main cuts of beef and the aurochs hide wrapped in skins, and their spears and knives were fastened again to their bodies, Wheaton pumped his fist and Noxon and the others rose up and walked down the back slope of the hill they had watched from.

Noxon stopped slicing time, so they could talk again. “Need to see any more?”

In answer, Wheaton played back his own recording of the event. “I hope I can slow it down or at least take it frame by frame because there’s so much to see,” he said. “But I got it. A thing of beauty.”

They had been speaking in low tones. But the Neanderthals hadn’t survived this long by being careless or unobservant. Noxon looked over and saw that the beef-bearing hunters had spotted them. And, enhanced as his hearing was by the facemask, he could hear them talking. It wasn’t a highly advanced ­language—it consisted of names and single words. “Who.” “What.” “Enemy.” “Kill.”

How the Wall had given him the ability to understand such fragmented speech—from Neanderthals rather than Sapiens—would be a matter for Noxon to speculate about later.

“Disappear but stay in this time?” asked Noxon. “Or return to the future?”

“I have everything I need here,” said Wheaton.

The Neanderthals had already dropped their burdens of beef and, with spears in hand, were running toward the observation party.

“Future it is,” said Noxon. “I might be able to do this without holding your hands, but let’s be safe.”

They took each other’s hands. The Neanderthals were so fast—Noxon could already smell them, not just their bodies but their breath, when he made a random jump forward in time.

They returned a few days before they had first arrived in the car. Not wanting to go through the tedium of time-slicing, Noxon flung them forward again. But the jump was imprecise enough that he overshot—now there were policemen and a tow truck at their car. They could probably have talked their way through the situation, but they would have had to explain why Noxon was fluent in Slovenian and how they had managed to camp for however many days the car had been abandoned. And then there was that lack-of-identification problem.

So Noxon jumped them back to a time soon after their own paths had disappeared over a hill, and they returned to the car long before their earlier selves would have reached the site of the Neanderthal aurochs hunt.

“We can’t prove that modern humans ever saw Neanderthals hunt that way,” said Deborah. “But Sapiens and Neanderthals coexisted so long that it would strain credulity to claim that they did not.”

“I agree,” said Wheaton. “My hypothesis isn’t proven, but this certainly didn’t contradict it. Right down to the picadors, that was a bullfight. And the birth of the sport of bull-leaping. Though the Minoan vase paintings show the bull-leapers going clean over the bull. Nobody seems to have tried to ride the things.”

“That had to wait for the rodeo,” said Deborah. “Such strength, such control, such patience. How could Homo sapiens have ever defeated these people?”

“They didn’t have to defeat them,” said Wheaton. “The fact that Homo sapiens has no mitochondrial DNA from Neanderthals suggests that if there were head-to-head battles, the Neanderthals always won, and their males mated with the Sapient women, never the other way around.”

“Or Neanderthal women were so strong that they broke the necks of any gracile humans who tried to mate with them,” said Deborah.

Noxon wasn’t sure he liked the relish with which she said that.

“Seeing all that bloody beef made me hungry,” said Deborah.

“Why?” asked Wheaton. “You always like your beef cooked into a flavorless stringy mass.”

“But I know that it begins with those great bloody haunches and sides,” said Deborah, “and I could do with a nice parmentier about now. Or a hamburger.”

“Well, Noxon,” said Wheaton, “in all honesty, today’s work completely pays for the easy half of the bargain—providing you with a place to stay while you wait to see why the people of Earth decide to wipe out your world. So if you want to stop taking me into the distant past, I’d still consider us more than even.”

“None of us would be happy without a visit to Homo erectus,” said Noxon. “Today’s excursion was its own reward.”

Wheaton laughed. “Here I am marveling at the athleticism of Neanderthal hunters, while the only reason I could witness it was because the human race has evolved an ability that nobody could have foreseen.”

“Cameras?” asked Noxon, feigning innocence.

Wheaton only laughed. While Deborah took Noxon’s hand and squeezed it. So it wasn’t all neck-breaking with her.

They decided not to fly back to the United States. Instead, they would go directly to Africa, and search for the paths of an early Erectus tribe. Not ninety thousand years, but nine hundred thousand, at least. Maybe twice that.

And this time, they would want to watch for days, not an hour or so. Neanderthal-watching had left Noxon exhausted. Erectus-watching would be far harder. But . . . it was all part of saving the world. And he was almost as eager to see what they might learn as Wheaton and Deborah were.

At the back of the plane to Nairobi, when they took a toilet break from time-slicing, Ram Odin asked him, “Are you up to this? It looked like that expedition really wore you out.”

“In Africa, maybe we won’t have to hike so far,” said Noxon. “And we’ll just watch for a few hours a day, then return to camp in the present. I won’t push myself too hard. And this”—he tapped the facemask—“helps keep me strong.”