A rock had fallen from the sky. When all was said and done, that's how simple it had been. Once upon a time, that had caused the end of the world.

Lysa leaned against the tunnel's rock wall to take a breather. She squinted toward the entryway and considered the too-bright landscape beyond. All of it had been underwater, once. So had everything. She reflected on the absurdity that the world was cycling back to a similar state.

A trickle of sweat slipped down her brow. Lysa squeezed her eyes shut, wriggling her forehead in an attempt to disengage the bothersome tickle. She was wearing gloves, and the rough leather was covered in grit and grime. Considering her work environment, she didn't trust her hands or sleeves to be clean.

She turned at the sound of gravel-crunching footsteps.

Danielle, a friend and colleague for the dig, gave a wave with one hand while shifting her shouldered burden. She was carrying a sack of mortar, heavy stuff, with the ease of an experience with labor.

Grime covered the younger woman's well-tanned skin, a testament to the length of their project. She'd hardly been a pale pink when they started. "Want me to get that for you?"

"Oh yes, please. It's driving me crazy."

The other woman leaned forward and raised a scarf wrapped around her neck. Her bright green eyes caught the light. She squinted while wiping away the offending sweat and smirked. "I told you to get one of these. Or at least a headband or something. You're just asking for gunk in your eyes."

"I know, I know. I'm just terrible at remembering." Lysa grinned. "But thanks, Dani. How are things going down there?"

"All done, just letting things set." Danielle patted the bag of mortar. "This one's extra, so maybe I'll build that barbecue I was thinking about."

"Cool! Hopefully this means we can restart the bore tomorrow."

That made Danielle wince. "Nawp, sorry. Liam said the inspector left for the day. Said he won't be back until next week. Three-day weekend for him, I think."

Lysa sighed. "Well, shit. That cuts things close. My permit expires on the fifteenth."

"I mean, would he really notice if you dig over the weekend? He only cares about the supports."

"Yeah, but I wouldn't trust him not to check the site logs. If Iker sees fuel reports through the weekend, he'll know we ignored our restriction. I can't afford the fine."

Danielle finally tired of holding the bag of mortar. Sliding it from her shoulder, she set it against the tunnel wall. Bits of the wall flecked away at the touch. The old mine was safe enough, but touching anything made it feel like the walls would fall apart.

"Well." Danielle wiped her own eyes with her scarf. "And maybe I'm crazy for making the suggestion, you could take some time off? Relax?"

"Eh," said Lysa, grumbling. "I should work on the write-up for this week. And send out invitations for next month's workshop."

"Come on, that'll take you what, a few hours? You've got all weekend. Liam and I were gonna head into Prescott for supplies. You could join us, have a decent meal." Danielle grinned. "I know you hate that pre-packaged junk in the trailer."

Lysa teetered on the edge of decision. She didn't think the bore would take much longer to reach its final depth. Setting up monitoring equipment would take longer, but this would be the sixth they'd installed during the trip. They had practice, and were an efficient crew.

Plus, she could finish most of the paperwork during the trip home. The drive would take several days, and her overnight stops would be perfect for catching up on documentation. "I guess I could do it on the road."

"Oh yeah, plenty of time there. Here back to Colby, ugh, that's five days? Four if you push yourself?"

"Yeah." Lysa rolled her eyes. As if on cue, her stomach chose that moment to growl. Betrayed by her own body. She shrugged. "Okay, fine, you convinced me."

"Yikes," said Danielle. "Don't sound so excited."

She smirked at her friend. "I am trying." She gestured toward the bag of mortar. "Need help with that?"

"Psh, girl. Get your ass down to the dig and shut everything down. And tell Liam to hurry with those measurements. I heard your belly rumbling."

"Okay, but don't say I didn't offer." Lysa turned away and turned on her headlamp. Back into the depths.

. . . .

Drilling could be dangerous work, and it was usually expensive and hard to protect. Do you buy a protective environment and seal away the dig site? How do you power your drill? What happens to the entry point after you leave? Does it get filled in so the next crew has to start from scratch?

An abandoned mine could be a perfect solution to several of those problems. If previous owners had kept to the bare-minimum of safety standards, you had a pre-built environment for geological research.

Plus, there were existing power lines running into the tunnels, and several of the mine junctions had pre-installed lighting. The dirty, half-working illumination was spotty at best, but it was better than working in the dark.

But best of all, a mine meant they didn't have to dig as far into the earth. That meant less money and less time.

Lysa had managed to secure long-term research permits for six abandoned sites. Well, two were partially-abandoned, but the owners hadn't cared about the dead-end shafts and were happy to get some return for their unrewarded hopes.

That had taken longer than the permits. Funding. Sixty-some thousand dollars had been allocated for the entire trip, and eighty percent had gone to the mine owners. Or local governments. Or taxes.

That had left little more than ten grand to fund equipment purchases, travel, and some form of lodging through the six-month trip.

Lysa was tired, and she was nearly broke, but she had accomplished everything they'd set out to do. With any luck, the results would make for a solid paper on modern data gathering in critical zones. She'd certainly been impressed with the combined data from new techniques in RADAR, LIDAR, and sample analysis.

Plus, long term they had new seismology stations added into the temporary network of sensors. With any luck, they'd prove reliable enough to serve as reference sources for the national seismic system. Lots of successes, lots of data to crunch, and good experiences with her colleagues.

It had been a great trip, and she was sad to near its end.

Her thoughts melted into a quiet state of calm as she continued through the mine. It wasn't a short trip, the hike down to the boring equipment, but it was easy enough. The site's original owners had put in rail and kept the exploratory shafts at an easy grade for walking.

There was a lot of quiet along the way. And cold. It was noticeably chilly after the first hundred meters. She enjoyed the escape from Arizona's heat.

Rounding a final corner, she smiled as she saw Liam at work in the main cavern. The lights were better in the wide junction, and the ceiling was a meter higher than elsewhere. No looming threat of bumping your head. Lysa pulled her headlamp down onto her neck and waved.

Liam didn't see her, and in fact seemed entirely oblivious to anything except his work. He had the LASER rangefinders in a new configuration since last time. His darks eyes were narrowed in a concentrated squint behind heavily-rimmed glasses. The man claimed to have great vision, but you wouldn't guess so by the way he leaned into every moment of observation. It was like watching Mr. Magoo peering at unfamiliar surroundings.

"Liam, you almost done?"

He didn't hear her, of course, because Liam was also wearing his headphones. He was always wearing headphones

Getting closer, Lysa could hear the tinny whisper of music. She waved in another attempt at catching his attention, but had already given up. She knew how much it sucked to be surprised after being alone in the dark caves. That, and she didn't want to disturb him while he crouched over the system panel.

Accurate measurements were critical to getting the sensors accepted for future research and reference inclusion.

So, seeing no reason to hurry, Lysa crossed her arms and watched. Liam was an expert with the measurement equipment, and seeing his process was a helpful reminder on procedure. He made an adjustment, then stooped over the readout, adjusted, stooped.

A flicker of color caught her attention. Across the room, a status light went green to amber. That was odd. Circling around Liam's side, Lysa walked to the boring terminal.

They had already installed the seismic monitor. As part of their tests, they wanted accurate readouts on the boring unit's seismic signature.

The display showed a warning light.

Lysa crouched and tapped the panel. She flipped through menu screens and went to the error logs.

'OOS: Tolerance failure.'

"Out of synch?" she asked herself. "What the hell does that mean?" Sighing, she pulled out her phone and scrolled to the operating manual she'd downloaded.

She peered at a section titled, "Troubleshooting Steps."

'OOS: Tolerance failure - The system is no longer synchronized with some or all of its external sensors. OOS faults usually indicate a significant increase in signal noise. Possible causes include improper grounding, loose sensor mounting, or faulty devices.'

Lysa stood up with a grimace. "Well, shit. And we just got this thing calibrated.

A hand clasped around her shoulder.

She jumped to the side with a shriek.

Liam stepped away with raised hands. "Sorry, shit! Sorry!"

"Fucking, fuck, Liam! You scared the piss out of me!"

He cringed. "Hopefully not literally. Sorry again."

Lysa put a hand over her heart and let out a long breath. "Gods, you asshole. And I just did all I could to keep from surprising you while you got your readings!"

"Oh, you've been here that long? Huh." He glanced toward the rangefinder array. "Yeah, those things are being a pain in the ass." His voice withered in volume. He was distracted.

"Huh. What do you mean? They've been working alright so far."

"Yeah, but it's like they're busted somehow."

Lysa winced. "Dammit. That's the last thing we need. Those are loaners. I can't give them back broken."

"Well, that's what's strange." Liam shrugged. "They don't really act like they're broken." He scrubbed a hand through his frizzy kinked hair. "Just. The readings aren't right. Maybe the sensors got dust in them?"

"Huh, I guess that's possible." Lysa glanced toward the seismometer. "The seismometer is acting up too, but I thought we kept everything sealed during the installation."

Her stomach suddenly dropped. A feeling like driving too fast over a dip in the road.

Liam shivered. "Whoa, that was weird."

"You felt that too? What just happened?" asked Lysa.

They felt it again.

And then, everything began to move. There was a terrible grumble that they could feel. The sound surrounded them, coming from every direction at once.

The lights went out.

Lysa shrieked out of some primal, pent-up fear beyond consciousness.

"Oh shit, oh shit, oh shit," came Liam's voice, and it grew distant and whispered and hollow with distance.

Something cracked, and the grumble rose in volume until it was a vibration and then a terrifying shaking of the surrounding rock. Nothing so solid was supposed to move so quickly.

"Liam? Where are you going? Where are you!?" Lysa held her hands in front of her, feeling, groping for something to hold onto, searching.

The ground itself tilted, or maybe she tripped on something, but the dark was too absolute to tell. Too late, she remembered the headlamp dangling around her neck.

Too late as she fell and tumbled across the quaking stone floor.

Something hit her, sudden and firm and pleasantly cool. She felt a stinging slap on the side of her head, saw too-bright stars, and then blacked out.

. . . .

Lysa woke aching in the dark. She made an attempt to move, and it was a relief that her body responded. She sat up with a groan. Dimly, she remembered what had happened.

"Liam?"

At first, she hardly believed that her voice was working. Everything felt muffled. Unsure if her own eyes worked, she remembered the headlamp and slipped it back to her forehead.

A flick of the switch bathed her surroundings in a blue-tint. She winced at the brightness.

Then she winced at her own legs. One pantleg was ripped below the knee. Her calf was badly scraped, already dried with blood, and one of her tan leather boots had a gouge in the side.

Around her, everything was dangerously close. Everything had collapsed. Lysa called out again, louder, "Liam?"

Still, nothing.

She felt something burning in her chest. It was a weight, heavy and with a thickness of pressure that labored her breathing. Closing her eyes, she sought calm.

Panic would get her nowhere, she thought. Panic will get me dead, she reminded herself.

Yet pain came with a rising calm. She felt aches and scrapes and bruises up and down her body. She would be sore for weeks.

If you live, offered her mind.

She shook her head and surveyed the miracle of her collapsed shelter. She was surrounded by boulder-sized shards of rock, but there were craggy gaps of shadow that might lead elsewhere.

Hopefully, she could squeeze her way back toward the surface. That gave her pause. She tried not to think how far she'd hiked into the mountainside.

Lysa really hoped the tunnels were still intact. She didn't have the food or water to last underground for long.

She crawled toward a gap in the jagged stone walls. Dead end. The next gap showed promise, but it was too narrow. Hardly wide enough for an arm.

One by one, she checked possible exits. A few were feasible, but she only took note before checking the others. She had already resigned herself to the weariness of backtracking through a maze of crumbling paths.

There were four choices at the end of her exploration. None looked any better than the other. Digging through her pockets, she pulled out a compass.

She gritted her teeth at the sight of its dancing arrows. Something was interfering, so she had no idea which direction to take. "Shit," she muttered.

Lysa sighed, rubbed a throbbing bump on the side of her head, and chose a random entrance toward more darkness.

. . . .

True silence, and true dark, were stifling absolutes. They pushed at the mind as if a physical presence. They wrapped Lysa in their emptiness. They stretched time and space so that each moment was an endless void of existence.

The only distraction was pain.

Lysa woke from the pain and tried to focus on the nothing of her surroundings. It took several moments to reorient, to remember, before she acknowledged her place in the world.

Still under tons of rock. Still wandering through the dark in a half-known mountain.

She flipped the switch on her headlamp and sighed from the relief of being able to see. Sleep had felt inevitable, but she had drifted off with nightmares of never waking.

Tired, dehydrated, and aching, she used the light to look for her next direction. It had taken four attempts, but she thought she had found the right path. The night before, or period before sleeping, she had passed a section of cabling that implied she was in the main tunnel.

Forward, then. Half-crawling, half-crouching, she moved toward a promising gap of collapsed debris.

Lysa winced as she scraped her shoulder on something overhead. A glance up, squinting in the glare of reflection, proved that the ceiling was getting lower. She dropped to her belly, wriggling, neck craned up to see forward.

The headlamp gave her a tiny slice of reality. The empty beyond was terrifying. It was hard not to imagine that all ended beyond the edge of light. So, she concentrated on moving forward toward the light that she projected.

Something, somewhere, gave a groaning pop. A faint rumbling drifted through the ground, but it ended within moments of starting. Nevertheless, the sound was nerve-wracking. Lysa had just enough space to inchworm through the opening of rock. If the cave-in shifted-

She turned her mind away from that thought. Instead, she focused on her knee and the sharp pain when it bent. She took note of the pulse of ache on her calf from the bruised scar.

Then she blinked. She was seeing things. It was faint, but she could swear that there was light ahead. A small pinpoint of blue.

Hopeful, she hurried ahead. Only to scrape both shoulders and knock her hip against an outcropping of rock. She hissed at the pain, but pushed past the obstruction.

Yes, it was there. The blue was something unnatural, something artificial, but it was light. She was so close to something different. It could be some old machine, or maybe it was a left-behind sensor, but it was a change from the nothing of her collapsed surroundings. That was enough to inspire a burst of eager energy.

One hand on the rough floor, one foot on the wall, she shoved herself onward. Twisted and rocked to escape the grasp of earthen fingers.

Until she couldn't.

She squeezed herself together by pulling in her shoulders. Kicked as if she could swim through the tunnel.

"Fuck," she whispered.

She was stuck. It took everything she could not to scream. With anger and anguish and terror. She wanted to anyway, but breathing suddenly felt impossible. Could she take a full breath? It felt like her lungs were compressed. Like she didn't have enough room to take more than gulp of air.

"Lysa?" asked Liam. He was somewhere ahead.

The voice almost made her scream anyway. She started to cry. She wasn't sure if it was relief or terror. "Liam? Oh, Liam, please! Help help help!"

That dot of blue stood up, and she realized what it was. His wireless headphones. Their little power light was going strong. There were footsteps, and then Liam entered the reach of Lysa's headlamp. "Gods! Lysa, you're alive! Thank goodness!"

She tried to extend a hand, but found she couldn't. She was wrapped up in wedged-together stone. Her elbows were pinned to her sides. "Shit, I'm so glad to see you. Help me! I'm so close to getting out of here!"

He crouched and twisted to get a closer look. "Can you go backward at all? Maybe change your angle?" He paused, eyeing the mouth of the passageway. "Might be you could come through on your back."

Lysa considered it, tried to feel where she could take hold. "One sec, lemme try." She shimmied herself away from the friendly face. It hurt, physically and emotionally, but it worked. She wanted nothing more than to burst through and give him a hug.

Another meter back, she found that she was less constrained. Free enough to twist herself around. "Okay. Coming back."

Knowing that she had a potential helper, she stretched out as much as possible. Extended her arms all the way forward. As if she could fly through the cramped space.

"Okay," said Liam. "I'm ready. I'll pull you out if I can."

Slowly, painfully, Lysa rocked from side to side. Centimeter by centimeter, she wriggled back toward the opening. She kept expecting to stop. She kept expecting the walls to close together and squeeze her, trap her, forever.

Then she felt Liam's hands close around her fingertips. Fumbling, then taking her wrists. "Okay, keep coming."

His help sped up progress exponentially. She still had to shift back and forth, but every bit of motion helped Liam pull her further into the open chamber beyond.

Finally, she was free. She lay in the dark, breathing too heavily, staring at a ceiling that was thankfully at standing height. It was all she could do not to shake herself apart.

"Hey, you okay?"

Rolling onto her side, Lysa got up and fulfilled her need for a hug. She half-tackled him in the glaring light of her headlamp. "I thought you were dead!"

"I thought you were dead!" He disengaged, carefully, and with a sigh. "But we're not out of this yet." He pointed into the darkness.

Lysa heard a detached defeat in his voice. Turning, she eyed a wall of stone.

Liam murmured. "That's the way out."