Imagine sucking air into a pair of lungs. The windpipe may bulge, but it never bastardizes its original proportions too much. The true change occurs around the lung sacs. As more oxygen and nitrogen enter a space too small, there is only one thing to do: expand.

  So long as internal pressure increased, so must volume. That's what the Gaiss Hollow looked like, the lung of a giant expanded to the point of bursting, and then some. This giant had long since died and returned to rest in stone. Its lung, petrified and reclaimed by moving sediments, has now made a subterranean world. This place was the only one Pa-5 had ever known.

  She saluted her guide as the scutumsteel slid back, collapsing into the valley wall. He returned it, and in his eyes she saw the same look the other guides and assistants had given.

  She was at the bottom of one of the crevice-like valleys dotting the landscape around Fort Io. Those valleys characterized the land west of the Last Light. Most were the result of drilling into what had once been territory enriched with ore veins.

  She clicked off the headlights. Safer to allow the dim, bioluminescent glow emanating from the local flora to guide her. Moss was the only thing that could survive down here without human intervention.

  Various species thrived in the valley basin with a determination rivaling cockroaches. She had once heard of a kind of plant called a flower; she imagined the plant as beautiful and otherworldly.

  The path flickered, rerouting as she turned. It led beyond the local fog. She proceeded, cautious at first. There was no way to know if there were any Aud that skirted around the fort as advance hunting parties. Most would've gone east, attracted by the capital's population and Fort Rhea.

  She lumbered along, cringing every time she stumbled against a rocky cropping. Narrowly avoiding face-plants became something of an art. Even if the modified light WAVs had designs for maneuverability and speed, she would've felt more at ease running unaided. Her body wouldn't have been as fast or enduring, but she didn't want to second-guess every step.

  She tried to adapt with every meter. Relying on her HUD and movement-automating protocols led to a delicate balance. She made her big trio speed, consistency, and balance.

  She was already occupied with micromanaging herself. She compensated by cranking the audio sensors above their recommended input. Her ears could serve as lookouts. Each footstep was a deep clomp in her ears. At this level, the fort's distant, ongoing defense was still audible. Mostly the war cries of the Aud, but the retort of sonics and cylinders made it through, too. Together, it was a macabre mixture.

  The number of man-made sounds decreased every few seconds. "They're paying a price for you. Move it!" she muttered to herself. The timer she imagined over her head was still there. It ticked with ceremonious indifference. She'd managed to push some of the shock from the attack from her mind, but it was still too much to make peace with.

  There had been drills, she mused. With two of the original forts nothing but history and ruins, it was never a if. The Aud would target another fort. The question was a matter of when.

  An unlikelier, yet still possible outcome was the Aud bypassing of the forts altogether. The sitesmen would only learn of the Last Light's fall days after. She supposed it was better, infinitely so, that another fort had met its end. If Rhea went down in carnage as well, at least the capital would remain standing.

  So long as that was the case, there was a chance for rebuilding and repopulation. With that would come an inevitable counterstrike against the Aud. If the Last Beacon fell, so would their last hope for the future.

  She stumbled as her leg slid into a pothole hidden by moss. At the end of the valley, she found a rock wall to lean on for support while she freed herself. The HUD beeped, and to her chagrin, she watched as the dotted line rerouted again, directing her up and over. Good thing they sent her off in a light WAV.

  The number of handholds needed to make a quick path up was scarce enough that she had to make a few risky maneuvers. Her knuckles punched deep into the stone whenever it wasn't enough. The only time she had to jump, the fear of gravity overpowering her was strong.

  "When I get home--" Right. She couldn't get her hopes up and risk making a mistake, especially not here. It was if. If she made it home, not when. The last step was another leap of faith, something she didn't do lightly.

  But the suit didn't fail. Providing a reassuring lack of error in its movements was what it did best. She dragged her torso and legs over the top, stopping to take a breath and look over the edge. The valley was further down than she first thought. The realization gave credence to her unwillingness to risk speeding up her climb.

  The HUD's track flashed, informing her of an emergency change in course. Someone further along another path, closer to hers, had sent out a warning. She wondered if it was someone she knew, pressing her knees into the crumbly sediment to stand.

  The "ground floor" of the Gaiss Hollow was an impossibility stretching for hundreds of kilometers. It was as if someone had displaced an entire region of great plains down here. Human scientists had long puzzled over how it was vast enough to have its own airspace. How the immense cavern roof hadn't collapsed without evident supports garnered much curiosity as well.

  Like the valley, the craggy ground itself was near imperceptible beneath the white. The blanket of fog refused to budge or disperse even as Pa-5 moved through it. It swirled and coasted around, but it never went higher than her thighs. Or, the WAV's thighs, at least. It'd be up to her waist if she stepped out.

  There were fewer mosses up here, too. Or any plant life. The path continued on and on, and despite her reservations, Pa-5 slowed her pace. The suit battery was down three percent. Unless she wanted to see the meter drop lower, she needed to get conservative.

  A case of content theft: this narrative is not rightfully on Amazon; if you spot it, report the violation.

  Out of the immediate vicinity of the valley, she halted long enough to deposit a cluster of stands. Each uncurled and began racing in a different direction like three-legged dogs. Inside her helmet, she watched as new feeds buzzed alive on her HUD.

  The scout drones had an enduring design, with a large enough internal volume to hold a suit battery. The smaller number of functions meant the drones could continue operating for days after her suit ran dry.

  Two went back towards the fort. One returned to the valley, waiting at the top of the ridge so she'd have forewarning for followers. Three went ahead of her in a pronged formation, the one in the middle heading straight along the HUD's path. And two more went off in the opposite direction, toward the Last Light. She expected the ones assigned to check the situation at the fort to encounter Aud first.

  Two kilometers along the path, an alert sounded. The fifth feed took priority on her HUD. It was the drone headed for the northwest, a good seven kilometers from her. Capturing some vague motions, the scout's programming switched to thermal recording equipment. It revealed a trio of hazy, red blotches crowded around another smaller blotch.

  She'd passed the threshold where Fort Io could warn her of a suicide runner's death. Or the fort had been overrun, and she was out of time. Whatever the case, Pa-5 took manual control of the drone, directing it to change course back east. She needed to see the number of Aud heading west, in her direction.

  While she covered more ground, she continued cycling through the feeds. Issuing instructions to the drones to inform her when they detected abnormal movement or heat emission came first. It wouldn't hurt to get a location on any of the surviving engineers while they were at it.

  One of the eastern drones past the fort encountered another drone model. It wasn't one of hers. Active, but unmoving. It had stopped receiving instructions from its deployer, she guessed. Did it belong to the pilot her west-most drone found?

  The trio of drones she sent back the fort's way had arrived. Two went to check the northern and southeastern perimeters. Her third moved into the fort itself. The walls still stood, but they had been so damaged it was a miracle they were still upright. The drone climbed up and over, and the scene she'd morbidly anticipated greeted her.

  Smashed and collapsed structures impeded its progress. It captured images of bodies left, right, and center, with more unmoving humans than Aud. A good chunk of stragglers were still around, gorging themselves on the bodies of both sides. Humanity knew the Aud practiced cannibalism, but watching a group of whites tear into a dead yellow upset her stomach.

  The drone utilized its anti-grav nodes to leap from the wall of one of the adjacent units. She wanted to get a fuller picture before risking the drone.

  The Aud had whittled down the imposing defense crews guarding the garage to two lines. Accompanying emplacement fire from behind was sporadic, unhelpful. They were still doing their best to hold the accumulated horde back. They used the height of the units in that section to their advantage, funneling the Aud into a choke.

  At this stage in the fighting, the reality had set in. WAVs that got dragged away from the defensive lines didn't resist or try to retreat. If they broke free, the pilots charged further into enemy-captured territory. The suits' battery cores received instructions to discharge their contents in an instant. Turning back, she realized she could see weak flares from the kamikaze bombs where she was.

  Those that remained wouldn't last much longer, either. The most pristine armor had a non-functioning arm. Most were so damaged the legs no longer worked. These WAVs sat against walls or turrets, relying on their armaments to make a futile contribution.

  Pa-5 had thought they could hold out for another couple of minutes. That would be enough time to gain another kilometer of breathing space. She chewed the inside of her cheek. Her hopes dashed themselves against rocks when she caught a glimpse of purple among the Aud.

  The majority of the attackers had been white and orange-furred. Which was why the fortress's defenders had lasted this long in the first place. The toughest orange wouldn't withstand a single hit from a Titan's emplacements.

  But the fort never held a titan in reserve. At least the WAVs had done well enough, coordinating their efforts even in a doomed situation. They trapped and systematically eliminated stragglers, simultaneously holding back the main bulk.

  But a purple-fur was as far as could be from the lower tiers. Mostly following a rainbow's organizational theme, the fur represented their threat level. The further along it was, the harder they were to kill. Their speed, strength, weight, and intelligence were all elements of consideration.

  The appearance of a purple Aud harbringed certain defeat, and in marched one, gaping maw and all. As it stepped forward, the fighting slowed. The rest of the Aud backed up. They shoved themselves onto either side, even if the combined bodies crushed those further behind.

  The two lines of WAVs grasped the lull in action to repair the formation. The purple looked up and down the line and took a step forward.

  "Overcharge nets, cone spread!" an officer cried.

  At his command, the pilots exploded into action. The rest of the horde lost priority in the face of an overwhelming threat. Static emplacements from behind launched netting, while the WAVs launched conductive cables. When they had the purple entangled in scutumsteel, the suits unleashed the power of their batteries. Some of the suits stuttered, and others fell over.

  The purple grunted and coughed up a bit of smoke. Nothing else. No sizzling. No charred fur. No convulsions. Just ten seconds hooked up to the raw power of a single suit core could fry the average human brain to putty. But from the collective discharge of dozens, the purple had endured a modest shock.

  It flexed, stretching out its hind legs. One by one, the fibers of netting snapped under the tension. When it was free, it bolted forward, a blur. It tore Five WAVs in its path asunder, trampled others, and tossed more into the air.

  The rest turned around in an attempt to restrain it, turrets swiveling in a desperate bid to lock on. Turning their backs was a mistake; the rest of the horde had lost the fear of an apex predator that held them in place.

  The last two defensive lines crumbled like a sandcastle. The screams were brief amid the roars, and all the drone could see was a frenzy of fur. She swallowed her revulsion and directed the drone to return to the outskirts. It wouldn't make it inside the garage without something crushing it underfoot. That was if it went unnoticed.

  "And s-so, Io joined his siblings," she recited a line from a children's book, "and nevermore drew breath."

  She marked down the time; the Directory would want as accurate a report as they could get. She wouldn't forget anything. It wouldn't do for them to catch her slacking. If she made it. If. If.

  The rest of the path to her destination was uneventful and, to her surprise, boring. She had clawed her way away from death's grasp multiple times in the last hour. Her heart was still racing, even if knowing that she should be safe for a half-hour, minimum, placated her.

  But that adrenaline couldn't last without a tangible threat to latch on to. So she used her thoughts to distract herself from the other ones. And she realized boredom was creeping in.

  She wanted to laugh. Boredom. Here she was, on her way to inform the last people in the world that the end was nigh, and she felt bored. It was disrespectful, completely and utterly, to every person who died at the fort. But not even shame could rein it in.

  Her HUD didn't leave her with her thoughts for long. "Notice: Arrival at quaternary checkpoint in three minutes. Addendum: Quaternary checkpoint: Greater Western Tunnel System."