Sally eyed Joshua. ‘I bet Helen wasn’t happy that you refused to go back with her.’

‘Look, it was tough on us. But Datum America is where I grew up. I can’t just abandon it.’

‘So you decided to stick around and use your stepping superpowers to help the afflicted.’

‘Don’t give me that, Sally. You’re here too. Why, you grew up in Wyoming itself—’

She was grinning. ‘Yeah, but I don’t have a little wife trying to draw me away. Big argument, was it? Or just one of her long sulks?’

He turned away, fixing his mask with an angry tug on the straps at the back of his head, pulling up his hood. She laughed at him, her voice muffled by her own mask. He’d known Sally for ten years now, since his own first exploratory jaunt into the deep Long Earth – only to find Sally Linsay was already out there. Nothing much about her had changed.

The National Guard kid positioned them by a strip of police tape. ‘The property you’ll be going into is right ahead of you. A couple of kids came out already, but we’re missing three adults. Record of one phobic. Family name Brewer.’

‘Gotcha,’ Joshua said.

‘The United States government appreciates all you’re doing.’

Joshua glanced at Sally’s eyes, behind her mask. This boy was no more than nineteen. Joshua was thirty-eight, Sally forty-three. Joshua resisted the temptation to ruffle the kid’s blond hair. ‘Sure, son.’ Then he snapped on his head torch and reached for Sally’s gloved hand. ‘You ready?’

‘Always.’ She glanced down at the hand holding hers. ‘You sure that fake paw of yours is up to this?’

His prosthetic left hand was a legacy of their last long journey together. ‘More than the rest of me, probably.’ They hunched over, knowing what was to come. ‘Three, two, one—’

They stepped into hell.

Ash and pumice pounded their shoulders, their heads, the ash like diabolic snow, grey, heavy and hot, the pumice coming in frothy pebble-sized chunks. The falling rocks hammered on a car in front of them, a mound already heaped up with ash. The background noise was a steady dull roar that drowned out their speech. The sky, under Yellowstone ash and gas and smoke from a plume that by now climbed twenty miles into the air, was virtually black.

And it was hot, hot as a pioneer town’s forge. It was hard to believe the caldera itself was all of fifty miles away. Even out as far as this, some said, the falling ash could melt again and flow as lava.

But the property they’d come to check out was right before them, as in the Guard’s plan, a one-storey house with a porch that had collapsed under the weight of the ash.

Sally led the way forward, around the buried car. They had to wade through an ash fall that was feet deep in places, like a heavy, hot, hard snowfall. Its sheer weight was only the beginning of the problems the ash caused. If it got the chance the stuff would abrade your skin, turn your eyes into itching pockets of pain, and scrape your lungs to mincemeat. Give it a few months and it could kill you, even if it didn’t just crush you first.

The front door seemed to be locked. Sally didn’t waste time; she raised a booted leg and kicked in the door.

Wreckage clogged the room within. Joshua saw in the light of his lamp that the load of pumice and ash had long overwhelmed this wooden-framed structure, and the roof and loft space had fallen in through the ceiling. This living room was cluttered with debris, as well as with grey drifts of ash. At first glance it seemed impossible that anybody could be left alive in here. But Sally, always quick to assess a new and confusing situation, pointed at one corner where a dining table stood, square and stout and resistant, despite a thick layer of ash on its own upper surface.

They pushed their way through. Where their booted feet scraped away the debris, Joshua glimpsed a crimson carpet.

The table was shrouded with curtains. When they pulled these aside they found three adults. They were just mounds of ash-grey clothing, their heads and faces swathed with towels. But Joshua soon identified a man and a woman, middle-aged, maybe fifties, and one woman who looked much older, frailer, maybe eighty years old; slumped in a corner, she seemed to be asleep. From the toilet stink that came out of this little shelter, Joshua guessed they’d been here some time, days perhaps.

Startled by Joshua and Sally in their nuclear-alert-type masks, the middle-aged couple quailed back. But then the man pulled away a towel to reveal an ash-stained mouth, red-rimmed eyes. ‘Thank God.’

‘Mr Brewer? My name’s Joshua. This is Sally. We’ve come to get you out of here.’

Brewer smiled. ‘Nobody gets left behind, eh? Just like President Cowley promised.’

Joshua glanced around. ‘You look like you did pretty well here. Supplies, stuff to keep the ash out of your mouths and eyes.’

The man, Brewer, forced a smile. ‘Well, we did what the sensible young lady said.’

‘What “sensible young lady”?’

‘Came around a couple of days before the ash fall really kicked in. Wore kind of pioneer gear – never gave us her name, thought she must be from some government agency. Gave us smart advice about survival, very clear.’ He glanced at the older woman. ‘She also told us very clearly that the planetary alignment was nothing to do with it, and this wasn’t a punishment by God, and my mother-in-law seemed to find that a comfort. Didn’t take much notice of her advice at the time, but we remembered come the day. Yeah, we did OK. Although we’re running out of stuff now.’

The middle-aged woman shook her head. ‘But we can’t leave.’

‘You can’t stay,’ Sally said harshly. ‘You’re out of food and water, right? You’ll starve to death if the ash doesn’t kill you. Look, if you don’t have Stepper boxes we can just pick you up and go—’

‘You don’t understand,’ Brewer said. ‘We sent away the kids, the dog. But Meryl – my mother-in-law—’

‘Extreme phobic,’ the woman said. ‘You know what that means.’

That stepping between the worlds, even if Meryl was carried over, would invoke such a reaction in her that it could kill her, unless a cocktail of appropriate medications was quickly administered.

Brewer said, ‘I’m betting you’re out of phobic drugs already over there, where you’re taking us.’

‘And even if not,’ said his wife, ‘the young, the healthy will be prioritized. I won’t leave my mother behind.’ She glared at Sally. ‘Would you?’

‘My father, maybe.’ Sally started to back out of the crowded space. ‘Come on, Joshua, we’re wasting our time.’

‘No. Wait.’ Joshua touched the old woman’s arm. Her breath was a rattle. ‘What we need to do is take her someplace where they do still have drugs. Somewhere away from the ash cloud zone.’

‘And how the hell do we do that?’

‘Through the soft places. Come on, Sally, if there was ever a time to use your superpower it’s now. Can you do it?’

Sally expressed her irritation with a glare through her obscuring facemask. Joshua stuck it out.

Then she closed her eyes, as if sensing something, listening. Feeling out the soft places, the Long Earth short cuts only she and a few other adepts could use . . . Joshua’s idea was that Meryl could be carried, via the soft places, to someplace other than a stepwise Bozeman, to someplace where the medications would be more freely available.

‘Yes. All right. There’s a place a couple of blocks from here. In two steps I can get her to New York, East 3. But, Joshua, the soft places are no easy ride, even if you aren’t old and frail.’

‘No choice. Let’s do it.’ He turned back to the Brewers to explain.

And the whole house seemed to lift.

Joshua, crouching under the table, was thrown on his back. He heard timbers crack and fail, and the hiss of the ash making still more inroads into the house.

When it settled, Brewer’s eyes were wide. ‘What the hell was that?’