Another, broader vent opened, and vomited lava.

Blue could smell sulphur and methane. Near the edge of the flow, loud cracks marked the explosion of methane gas. The fume clouds above the vents glowed orange against the blackening sky.

Blue?

“Sixt, I think it is starting. It was very sudden.”

He checked his cameras and instruments were stable, and that his data was indeed reaching orbit.

Then he pulled up his protective hood, and patiently described all he saw, as the Scottish ground — under intolerable strain — broke apart.

As it receded after its separation, Arkady had kept the spindly lander in sight through the eyepiece of the twenty-eight-power sextant. With its bright colours, white and gold and black, hanging in the shadow of the Moon, it looked something like a tropical fish, angular and unlikely.

But there were Geena and Henry in their snow white suits, perched on top of the Shoemaker platform. He could see them move as they worked their controls, or turn to each other and gesture: human beings, interacting as humans always had, here in lunar orbit.

When Geena fired the descent engine to drop out of circular orbit, Arkady was looking into the Shoemaker’s engine bell. The craft seemed to become a glowing ball, like a jet plane on afterburner, and it moved away from him as steadily as if mounted on rails.

The engine glow lasted a half-minute, then died, and he could no longer see them. Soyuz sailed on, through light, through darkness.

The engine throttled down, and cut. Suddenly Henry was falling again, and once more he felt his lunch rise up his throat. He swallowed hard.

Geena said, “Right on the nose.” She looked across, and he could see her face framed by her helmet. “We’re still breathing, Henry.”

“Maybe you are… Oh, shit.”

For now they were falling, tracking their ellipse, all the way down to the orbit’s low point at fifty thousand feet. And he could sense their diminishing altitude. The tightly curving edge of the Moon seemed to flatten, quickly. The features beneath him fled behind him, like shadows on an ocean.

He felt as if he had fallen over the lip of some giant, invisible roller coaster.

“And I always hated roller coasters,” he muttered.

Geena looked across at him. “I know,” she said. “Hold onto your ass, kid.”

“I’m holding.”

Earth rose ahead of them, unnaturally quickly, its blue making a contrast with the tan and grey lunar plains that was almost painful to Henry’s eyes.

…Shoemaker, Houston. We’re standing by.

“Houston, Shoemaker, reading you loud and clear, do you read me?”

Copy, Geena, good to have you back. That’s AOS, reading you five by. Coming up on twelve minutes to next ignition. We’re waiting for your burn report.

“The burn was on time. Residuals are minus point one, minus point four, minus point one. Frank, everything went swimmingly, just beautiful.”

The horizon closed in. Mountains hove over the edge of the world, chains of them, that curved inwards until Henry could see they formed a crater rim, and then, as soon as the far side was visible, the rim fled beneath him. Sometimes they flew over fields of boulders, immense, round-shouldered, their shadows long and flat.

“Look at that,” Geena said. “Some of those babies must be five storeys high.”

No, Henry thought. Probably ten times that…

It was strange to remember how he’d griped about the restricted viewing from the Soyuz. Now he could see too much, a three-hundred-and-sixty-degree span of Moonscape and sunlight and bare, clutching rock.

Under the control of the computer the thrusters fired. There was no noise, but Henry could see little showers of exhaust crystals venting into space, feel the punch of the burns through his feet and hands. The Shoemaker rocked from side to side, fore and aft, sharply; it was a stomach-jolting feeling, like turbulence in an airliner… but there was no turbulence here.

They reached the centre of the Moon’s daylight face, and passed beneath the sun. Giant pumice-grey lava plains fled beneath him. Briefly, at the subsolar point, the shadows disappeared, and the surface detail washed out.

Coming up on five minutes to ignition.

“Five minutes, copy.”

You’re heading right for the guidance box at perilune.

“Copy that.”

Shoemaker, Houston, you’re go for powered descent. Your signal is breaking up. Recommend you yaw right ten degrees and reacquire.

Geena pulsed her thrusters once more, and the Shoemaker swivelled, pointing its main antenna more squarely at the blue sliver of Earth.

Three minutes to PDI. Two minutes forty seconds…

“Forty-seven thousand feet. The laser altimeter has locked in. It agrees closely with the trajectory.”

Good to hear it, Geena. You’re looking good at three minutes. You are still go to continue to powered descent.

“Copy that…”

Now they flew deeper yet, over a mare, a lava plain. It looked smooth as wet clay, pocked here and there by small round craters, fleeing beneath them. This was the Mare Imbrium, he thought with a thrill of understanding: he was flying over one of the Solar System’s greatest impact basins, the right eye of the Man in the Moon.

Forty thousand feet high: back on Earth, even Concorde flew higher than this. No big deal.

But this was no airplane ride.

Tracking around the airless Moon, they were still following an orbit, and by dipping down from the peak of their ellipse they had actually picked up speed. They were moving at all of three thousand seven hundred miles per hour, more than a mile a second, five times the speed of sound. No pilot in history had flown so fast, so close: at orbital speed, hugging the ground.

Henry felt as if he was bare-ass naked, strapped to his table. He shut his eyes, clung onto his restraints, and tried to forget where he was.

“We’re drifting off.”

He snapped open his eyes. “What?”

“Something spooky. It’s as if the Shoemaker is trying to line itself up towards the radius vector.” Geena turned to him, her face mirrored. “It wants to point straight down.”

“I can’t feel anything.”

“It’s too subtle to see. The instruments know, though.”

“The mascons,” he said. “Mass concentrations. The Moon is a lumpy old world. It’s plucking at us. Playing with us.”

She grunted. “I wish it would leave us the hell alone. I sure wasn’t expecting turbulence out here.”

“Turbulent gravity… Oh my,” he said, looking ahead. “Oh, my.”

Aristarchus himself was shouldering over the horizon.

The crater’s walls were a great rampart, visibly circular, which rose out of the Imbrium plain like the walls of some impossible city. And already Henry could see Jays Malone’s rille: Schröter’s Valley, a dry valley gouged into the sandy surface of the Moon by a brief, late spasm of lunar volcanism.

The crater stunned him with its magnitude. The energies that had gouged out this monster — shattering the rock and melting the very floor — had been truly stupendous, far beyond human capability, as far ahead in the future as he cared to look. And yet, he knew, even this great impact had been a pin-prick compared to the gigantic, primeval events which had gouged out the great basins, the final formative bombardment that had shaped the geology of the Moon.

It was as much as humans could do, he thought, to send them this far, two tiny people, encased in air and water, descending cautiously on their candle-flame. How could they hope to shape events here, on this cosmic battleground?

The whole exercise, his grandiose, half-formed schemes, seemed futile before they even started.

But now the Powered Descent burn began, this toy lander’s rocket engine jarring to life once more.