He walked forward, towards the rille. He went over a smooth crest, and started descending into the rille itself. But there was no sharp drop-off; like every other surface here the rim was eroded to smoothness, and the footing was secure. The rope trailed behind him, reluctant to uncurl and lie flat in this weak gravity.

Just to be sure of his footing, he clambered back up the slope. There were no problems.

He turned, and bounded several yards back down the slope. Even from here he couldn’t see the bottom of the rille; it was still hidden by the broad shoulder of the valley.

The footing was good here. The Moon, shaped by impacts, was littered with rocky rubble. But this close to the edge, a lot of those fragments would have tumbled into the rille, carrying off the dust, and that had left the regolith here very thin—

Suddenly his left foot disappeared, out from under him.

“Shit.”

He looked down with surprise. His leg was just sinking into a pit of soft dust, softer and deeper than any other place he had come across, anywhere on the Moon.

He brought his right foot forward, but he caught it on a rock, and he fell with some force onto his hands and knees. His leg came loose of the dust pit, but his momentum rolled him forward, and the roll carried him over on his right-hand side.

“Henry. Are you okay?”

“Just a little soft here. I caught my… I stumbled over that rock.”

“You need me to help you?”

“No.”

He pushed his way to his feet, bouncing upright like a mannequin. He stepped back a little way from that patch of soft dust. It was a rough disc, he saw — and it swirled, gently.

Just as he’d seen in Scotland, on another planet, just as he’d predicted, he had found it here.

“Henry?”

“I’m fine.”

He carried on down the slope, following the tracks of Jays Malone as he had searched for his piece of lunar bedrock.

…And then he saw it, sheltering beneath a hummock in the regolith: an irregular-shaped crater in the regolith, scuffed by footprints. It was the original resting place of sample 86047, here on the Moon, a rock that had travelled a quarter-million miles from this spot, to his lab in Edinburgh.

He bent sideways, awkward in his suit, and ruffled the surface of the regolith with his fingertips, with reverence.

Then he straightened up. The tracks didn’t go any further, any deeper into the rille. The ghosts of Apollo couldn’t help him any more; and when he passed out of line of sight of Geena he wouldn’t be able to speak to her. Now, at last, he had to go where no human had travelled before.

He raised his gold sun-visor. For now, he wouldn’t need it.