It was a lot harder than it had been before. The thirsty regolith had soaked up the rainwater to a depth Henry hadn’t anticipated, and the wall had pretty much turned to a shallow slope of slippery mud. It was impossible to get a footing, or to grip with gloved hands, and they slipped back almost as much as they made headway. After a few minutes, Henry dumped his mud-caked gloves in frustration, despite Geena’s admonitions.

Eventually Geena found a way of zigzagging up the slope, like a mountain path: it was longer, but her footing held in the low G long enough for her to take each step and climb a little further.

Henry sought a more direct route. One of the many landslips had exposed a gutter of lunar bedrock. Henry found he was able to run at this, scrambling at the rock to get purchase before his feet slid out from under him, until, by sheer momentum, he’d reached the top of the rille.

Side by side, panting so hard their oxygen masks were steamed up, they stared out over the Moon’s new landscape.

It was a drab, muddy plain.

The sky was a steel-grey lid, laden with water-vapour clouds, clamped over this subtly curving sheet of red-brown mud. Here and there, Henry could still make out the overlapping craters which had populated this landscape — some of them had filled up with water, so the land was dotted with circular lakes, rippling sluggishly — but many of the crater walls had slumped. It was like standing in the flood plain of some unruly river.

The landscape was all but unrecognizable from the way it had been just a couple of days earlier.

A wind moaned, soft but guttural. And he thought he could hear thunder, somewhere around the curve of the world — maybe halfway round the planet, he thought; this was still a small world.

Geena was working her way around the Lunar Rover. It was a sorry sight: half tipped up into a flooded crater, its aluminum surfaces streaked with mud, its wire-mesh wheels sunk deep into the soggy surface. The big umbrella-shaped S-band antenna had slumped to the dirt, under the weight of the water which had pounded into it.

Geena got hold of the control column and tried to lift the Rover out of the mud.

“It wouldn’t work now even if you dug it out,” Henry said. “Those wheels—”

“I know.” She peaked a hand over her eyes and looked east, towards the old Apollo site. “We ought to go over there,” she said. “I bet the rain has made a hell of a mess.”

“I bet.”

“The flag, for instance—”

He bent down and was pulling off his boots.

She said, “And what the hell are you doing now?”

“What does it look like?”

“Are you crazy?”