All these instruments were improvised from lightweight gear deployed by VDAP to gather real-time data on volcanic events. It was true that what he was investigating here was no volcano, but even volcanology was a young science; he hadn’t had any smarter ideas on what to bring here, to this infestation on the Moon.

He actually enjoyed setting up the science gear: plugging cables into their sockets, testing power couplings and data transmissions. It was simple work, no more complex than putting together a back-yard barbecue. Yet it was good for his soul to have some familiar tasks to get through, here amid all this strangeness. He moved between the instruments, the fans of his backpack whirring, the oxygen blowing cool over his face.

When the science station was set up, he stepped back from it, towards the edge of the basalt ledge. He ran his eye over the connections one more time, making sure he hadn’t missed something dumb, checking all the power lights were switched on. He didn’t want to have to come back down here and fix anything.

However, it all looked fine. Now all he had to do was climb out of here, trailing a comms link cable behind him, so the station could talk to the surface, and so to Earth and the shelter.

But there seemed to be a softness, beneath the tread of his right foot.

He looked down sharply. He was maybe four feet from the lip. But suddenly the rock surface was crumbling like wet sand.

The last three or four feet of the ledge just disappeared, in a half-circle extending maybe a yard around him. Under a surface of some kind of duricrust, he realized, this whole ledge was rotten with Moonseed dust. Suddenly he was falling, amid a cloud of dust, and there wasn’t a damn thing he could do about it.

Moonseed sparkled in the light of his torch.

Falling on the Moon:

Dreamlike slowness.

In the first second — the first one or two rattled heartbeats — he only fell through a couple of feet. He fell stiffly, his suit starfishing around him, as if he was in some body-shaped coffin.

Two seconds, and, picking up speed inexorably, he had fallen ten feet. The rope was coiling behind him, still fixed to his waist. How much was there left? Enough to stop him hitting the Moonseed river?

Would he just drag his anchor rock off the lip of the rille after him?

Three seconds, maybe twenty feet, and at last his speed was becoming respectable. No air here, so no terminal velocity; if there was a hole all the way to the centre of the Moon you would just keep on falling, accelerating steadily, until—

His feet hit the surface of the Moonseed river.

It worked its way up his legs, to his waist, sluggish ripples spreading out from him. His speed slowed rapidly as the resistance of the dust built up. He could feel the pressure of the dust on his legs, crumpling the inflated pressure suit.

Now he was sinking slowly, as if into treacle. He tried to keep his arms out.

Up to his waist. He couldn’t move his legs.

He would presumably reach some level at which he would be buoyant. The dust was all but a fluid; Archimedes” principle would work, even here. How deep would that be? So deep that the pressure of the dust would crack his visor, ramming itself into his mouth and nose and eyes? Or maybe the end would be less spectacular: eventually, the heat trapped by the dust would surely kill him… The dust was up to his chest now. But his rate of descent was slowing. He tried to kick at the dust; maybe if he could lie on his back he could float like a swimmer on the Dead Sea. But he couldn’t move his legs, not so much as an inch; it was as if his pressure suit was embedded in concrete.

But the rope was taut, pulling at his waist. Geena. She was trying to drag him out of here.

He lifted his hands, and grabbed at the rope which snaked out from his waist like an umbilical cord. He could feel the tension; he imagined Geena at the surface, hauling, digging her feet into the regolith.

It was working. He could feel the dust falling away from his legs. Maybe he was out of it already.

He kept pulling, and Geena kept hauling, and he could feel himself rise with dreamy grace. Maybe he was going to live through this after all…

But now he became aware of a new problem. He couldn’t hear the pumps and fans of his backpack any more, nor feel the breath of oxygen over his face.

When he looked down at his chest panel, there was nothing but red lights. The heat, the pressure of the dust had killed it.

But right now he felt fine. Better than fine, in fact. He felt alert, confident. When he looked up above, he could see a line of white light, the sunlit upper face of the rille. Actually, he felt a little high.

He had no doubts, suddenly, that he would live through this; in a couple of minutes he would be with Geena, and then back to the shelter, and Earth, and in a few years it would be no more than a sea story he could share with Jane…

He was flat against the rock face, being dragged upward, almost passively.

Now he was approaching daylight. He was being hauled up the shallow upper slope of the rille, like a swordfish being landed on some Greek island beach.

He seemed to be lying on his back. The sun, a ball of white light, flooded his helmet. He turned his head towards it and let all that pure light pour into his open eyes. It was really quite beautiful. And there were colours, like the kaleidoscopic sparkle of a granite thin slice in his petrological microscope, all around him, the colours of the Moon.

But now there was somebody before him, a snowman figure loping around him as if in a dream. He — or she — reached down and closed something over his face, and the world turned to gold.

He closed his eyes.

Gold, grey, black.

Henry’s backpack was just a ruin. Crushed and overheated. Even his emergency oxygen supply, from the purge tanks, seemed to have failed. He was clearly suffering hypoxia. A few more minutes of this and he would suffer permanent brain damage.

Geena dug hoses out of her backpack. She coupled her own emergency air supply to Henry’s. That would be enough for an hour or so. Then she hooked up more hoses so Henry could share her supply of cooling water; he’d broil before they got back to the shelter otherwise.

She was tempted to peer into his helmet, to see if he was breathing, if he was responding. But it wouldn’t do any good. What could she do, take off his gloves to see if his fingernails were blue?

She pulled him up. He half-stood, inert, like a statue, so stiff was his suit. She managed to get his arm over her shoulder, her arm around his waist. Under lunar gravity he only weighed a couple of stone, but he was awkward, a stiff, massive shape. As she hauled him back towards the Rover, his feet dragged in the regolith.

It was going to be a race back to the shelter, to get Henry inside before that emergency pack expired. At least driving back would be easier. They only had to follow their own tracks back, to be sure of their destination.

But if anything else went wrong — if a fault developed with her own backpack, or the thirty-year-old Rover — it was quite possible neither of them would live through this.

She tried to hurry, forcing Henry forward, across the slippery regolith.