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.

Clutching his equipment, trailing the rope behind him, he marched on down the slope, into the shadow of the rille wall, alone.

It was dark here, the only light scattered from the far side of the rille.

He lit his helmet torch. It cast an ellipse of light on the regolith surface before him, and back-scattering illuminated a short way beyond that. He had to keep his head down so the light showed him where his feet would come down, so he could see only a few feet ahead of himself at any time.

He was truly, he thought, approaching the heart of darkness.

At first he moved cautiously. But the slope here, sandblasted by micrometeorite rain, was still gentle. Walkback limits, he thought; he could afford to go a little faster.

He lengthened his stride. Soon he was bounding in slow-motion leaps, sailing over the rocks and dust. When he landed he sent up sprays of dust which collapsed back immediately to the surface, like handfuls of gravel.

The trick with the light now was to keep it focused on the spot he was likely to land, rather than directly under his feet; it took some coordination, but he was getting the hang of it.