Emma looked up at Manekato, and she looked into her own heart. “Not yet,” she said.

There was a moment of stillness. In this open space the sun was warm on her face, invigorating, its light making the dusty air shine. The infant Nutcracker gurgled and plucked at Emma’s sleeve.

Manekato walked to the lip of the tunnel. She stood silently, on crimson earth, peering into the well in the Moon, its diffuse light picking out the folds in her blue-black skin. Emma wondered what she was thinking, what the tunnel was saying to her.

Mane turned. “It is time.” She held out her hands.

Yes, Emma thought. Somehow she knew it too. She stood up, brushing dust off her coveralls. The Nutcracker child clambered up into her arms. She settled her distorted head against Emma’s chest and promptly fell asleep.

Nemoto stood reluctantly. Emma could see she was trembling, utterly afraid.

Mane took Emma’s hand, and Nemoto’s, and Julia took Nemoto’s other hand. Cradling the infant, Emma walked up to the lip of the well.

The shaft at her feet was a cylinder, walled by what looked like sparkling glass, a wall that receded downwards to infinity. Lights had been buried in the walls every few yards, so the shaft was brilliantly lit, like a passageway in a shopping mall, the multiple reflections glimmering from the glass walls. Conduits snaked along the tunnel, their purpose unclear. The shaft was vertical, perfectly symmetrical, and there was no mist or dust, nothing to obscure her view.

Momentarily dizzy, Emma stepped back, anchored herself again on the surface of the Red Moon.

Nemoto said, “What is this?”

Mane said evenly, “It is a tunnel in the Moon.”

“But what is it for?”

“We don’t know.”

Emma said, “How deep is it?”

“We don’t know that either,” Manekato said. “We have tried sending—” she hesitated ” — radio signals and other emissions into the well. No echo has returned.”

“But,” said Emma, “it can’t be longer than the width of the Moon. Even if it came out the other side… It can’t be longer than that.”

“We don’t know,” Mane said. “We did not put it here.”

Nemoto said tightly, “What do we have to do?”

Mane regarded her with her large eyes, pupils black, the whites flecked with yellow. “I think you know.”

Yes, Emma knew — though she didn’t understand how she knew. A prickly wave of vertigo swept over her. Malenfant, she thought desperately, you should be here to see this. You would love it. But me…

There was no more time, no time for thinking, for doubt. Without a word, the five of them stepped off the lip of the tunnel, into the air.

For a moment they floated there in space, bathed in the light from the heart of the world, like cartoon characters for whom the laws of physics are momentarily suspended.

And then they began to sink, gently.

There was nothing beneath her feet. The air was full of light.

Slow as a snowflake, tugged by a force that felt like gravity — and yet it could not be gravity — Emma fell towards the heart of the Moon. There was no noise save the rustle of clothing, their soft breathing, no smell save the lingering iron-and-blood stink of the crimson dust of the Red Moon.

She could tell she was falling. Lines in the wall, like depth markers, were already rising up past her, mapping her acceleration. But it was as if she were suspended here, in the glowing air; she had no sense of speed, no vertigo from the depths beneath her.

She could hear her own heart pound.

Nemoto was laughing, manic.

Emma held the black bundle of fur closer to her chest, drawing comfort from the Nutcracker’s solid animal warmth. “I don’t know what the hell is so funny.”

Nemoto’s face was twisted, a mask of fear and denial. “We are not in the hands of some omnipotent, infallible god. This is no more than a gadget, Emma. More ancient than our species, more ancient than worlds perhaps, very advanced — but very old, and cranky, and probably failing as well. And we are relying on it for our lives. That is what strikes me as funny.”

Their speed picked up quickly.

In seconds, it seemed, they had already passed through the fine layers of the Red Moon’s outer geology. Now they sailed past giant chunks of rock that crowded against the glassy, transparent tunnel walls like the corpses of buried animals.

“The megaregolith,” Nemoto murmured. “In the later stages of its formation this little world must have been just as bombarded as our own Luna. Under the surface geology, the craters and cracks, this is what you get. Pulverization, shattered rock, mile upon mile of it. We are already far beyond the reach of any human mining, Emma. We are truly sinking deep into the carcass of this world.”

Mane regarded her, curious, judgmental. “You are analytical. You like to find names for what you see.”

“It helps me cope,” Nemoto said tightly.

The material beyond the walls turned smooth and grey. This must be bedrock, Emma thought, buried beyond even the probing and pulverizing of the great primordial impactors. Unlike Earth, on this small world there had been no tectonic churning, no cycling of rocks from surface to interior; these rock layers had probably lain here undisturbed since the formation of the Red Moon.

Already they must be miles deep.

Despite the gathering warmth of the tunnel, despite her own acceleration, she had a sense of cold, of age and stillness.

She had no real sense of how long she had been falling — it might have been seconds, or minutes — perhaps time flowed as deceptively here as space, as gravity. But she was reluctant to glance at a watch, or even look up to the receding disc of daylight above. She was not like Nemoto, determinedly labelling everything; rather she felt superstitious, as if she might break the spell that held her in the air if she questioned these miracles too hard.

They dropped through a surprisingly sharp transition into a new realm, where the rock beyond the walls glowed of its own internal light. It was a dull grey-red, like a cooling lava on Earth.

“The mantle,” Nemoto whispered. “Basalt. Neither solid nor liquid, a state that you don’t find on the surface of a planet, rock so soft it pulls like taffy.”

Soon the rock brightened to a cherry-pink, rushing upwards past them. It was like dropping through some immense glass tube full of fluorescing gas. Gazing at that shining pink-hot rock just yards away, Emma felt heat, but that was surely an illusion.

The baby Nutcracker stirred, eyes closed, wiping her broad nose on Emma’s chest.

Falling, falling. Thick conduits surrounded them now, crowding the tunnel, flipping from bracket to bracket. She wondered what their purpose was; neither Nemoto nor Mane offered an opinion.

For the first time she felt a lurch, like an elevator slowing. Looking down along the forest of conduits, she could see that they were approaching a terminus, a platform of some dull, opaque material that plugged the tunnel.

She asked, “Where are we?”

Mane said, “Thousands of miles deep. Some two-thirds of the way to the centre of the Moon.”

They slowed, drifting to a crawl maybe a yard above the platform. Emma landed on her feet, still clutching the infant — an easy landing, even if it had reminded her of her involuntary sky-dive.

Now she glanced at the watch Nemoto had loaned her. The fall had taken twenty minutes.

The smooth surface was neither hot nor cold, a subdued white, stretching seamlessly from one side of the shaft to the other.

Emma put down the infant Nutcracker. With a happy grunt the infant urinated, a thin stream that pooled on the gleaming floor.

In this place of shining geometric perfection, all the hominids looked misshapen, out of place: Julia with her heavy-browed skull, the Daemon with her looming gorilla body, her fast, jerky motions and her eerily swivelling ears, and Nemoto and Emma, the proud ambassadors of Homo sapiens, huddled close together in their dusty, much-patched coveralls. We are barely evolved, Emma thought — even Mane — unformed compared to the chill, effortless perfection of this place.