That had been her second mistake.

  Her uncontrolled lunge smacked her into the bottom of the tunnel, and then she fell. The HUD blared in her ears, and the LEDs within the helmet were a vibrant, flashing red. While she flailed, the HUD activated an emergency override, taking control of the suit. One of the YJs. She could remember which specifically if she wasn't tumbling through empty air!

  The left mount launched one more explosive. It adjusted the duration until detonation by microseconds before launch, shortening the timer. Doing that displayed processing speed she could never match.

  An eruption sounded from below. Both the greater and lesser tunnels acted like parts of a grand, enclosed space. Though that couldn't be true. They had to come out somewhere. To open air. True open air. A sky.

  She wrenched her mind away from daydreamt thoughts brought on by shock. What mattered was that she was in an enclosed space. That meant the suit could create a vicious updraft that slowed her fall. Just long enough for the suit to dig its knuckles into the nearest rock wall.

  Before, they would've torn through like sand falling through a sieve. But with the slower descent, the suit's power could pierce the rock. With the right amount of pressure and at the right angle, she could prevent any more lost height. She got jarred from it, but both her elbows and shoulders remained undislocated. Miraculously.

  Pa-5 looked down, heartbeat bludgeoning her ears. She couldn't see anything below, the darkness swallowing up the suit's headlights. Could she drop a flash cylinder and have her HUD grab post-flash images of the terrain below? Hmm, yep...no.

  In the near-darkness, the Aud already held the advantage. If she used a strong light source, she'd be trading vision for safety. It'd be a beacon in the dark. On second thought, she already was. She shut off her headlights.

  Plus, after the excitement of the fall, she'd remembered she used the last flash cylinder on the purple. "Can I climb back up?"

  "Addendum: Target rock wall leads to same compromised tunnel above. Material composition holding stalactite structures in place incapable of supporting WAV's prolonged weight. Notice: If disturbed, compromised structures will reach current position on average ballistic trajectory. Estimation: Implementation of proposal fails to preserve current safety parameters at eighteenth percentile."

  It fueled Pa-5's frustration. What was she supposed to do, hang here until a lucky Aud found her? Before she could think of something else, the HUD forwarded its own plan. "Advisory: Continue vertical descent. Addendum: Corrosion of target rock wall's integrity lessens further down.

  The HUD transferred more power from the core to the optics to support her night vision. Waiting while it fiddled with the settings left her feeling helpless. A few times, her auditory sensors registered noises that she was sure were from Aud climbing below her. All they'd need to do was venture a bit higher, or look up, and she could say goodbye.

  Not that there was anyone around but her HUD to say it to. Once she could see the rock wall comfortably, the HUD activated the new path. A series of handholds and footholds that could bear the WAV's weight flared new neon outlines.

  Pa-5 adjusted herself, climbing through the only space she could access. The rock wall crumbled like a thin film, and she lodged her feet through it deeper. She waited until the shifting stabilized and moved to the next position. It contorted her leg awkwardly inside the armor. It hurt less than her ribs, so there was that.

  She was making good progress when she noticed movement in her periphery. She froze. The HUD was quick to affirm her decision. "Notice: Green fur detected sixteen meters to right. Advisory: Remain still. Upon discovery, utilize explosive to distract."

  And then what? Jump down the rest of the way and hope the impact didn't crush her inside the WAV like an egg? There was anti-grav padding on the inside, true. It kept her body centered and prevented it from leaning too much on any particular area on the inside.

  But it had limits. It would protect her up to a certain threshold, and after that, she could only toss up her arms and hope for the best.

  In the seconds left before the green noticed her, she went through her inventory. She had two orbs left. Like all WAVs, her suit had pairing blades in each wrist and sonics mounted within the shoulders. She'd had no reason to use them until now. She was still running a retreat, not a guerrilla campaign. Maybe if all the suicide runners had stayed together?

  She gave the area of the rock wall the green-fur ripped to shreds as it climbed a prospective look. "HUD?"

  "Addendum: Jarring impacts with enough force may push stability of target rock wall over its threshold."

  That was what she wanted to hear. Although that area wasn't near the compromised areas where she'd come from, it wasn't that much more stable. Closer to fragile than what the normal integrity should be.

  She wore a strained smile while concentrating. Her right shoulder pauldron twisted in its socket. The sonic implanted within came to bear on the Aud.

  The sonics line of defensive weaponry employed by the First Ray was powerful. As powerful as they could arm their pilots with, without creating a resource deficit. Even the emplacements slotted into light WAVs could stagger a blue-fur. In a perfect world, that'd be enough to bring them down.

  Too bad she didn't live in one. At best, they'd stay disoriented long enough for a second shot from a supporting pilot to hit. All by her lonesome, Pa-5 would only get a single shot off before a whirlwind of death was upon her.

  But there was one thing she knew lots of pilots didn't think about. To stagger an Aud at all, sonics were powerful. It was just that an Aud was even more so. Using direct comparison made the weapons humanity relied upon seem faulty in comparison. Weak.

  She wouldn't aim to attack the Aud itself. It wouldn't fall if she did that, and that'd reveal her location. Sonics were loud, so who cared if they emitted no muzzle flashes? But what about its perch?

  The mount shifted again, aiming lower until it had a clear lock-on to the rock wall beneath the green's belly. She sucked in a breath. Felt the tension in her chest build. Held it until she was ready to burst, watching the Aud crawl closer.

  Trigger discipline was all that kept her from firing prematurely. Her target was completely unaware of the prey lying in wait mere meters away. She released the breath and felt the burn cool. And fired.

  This story originates from Royal Road. Ensure the author gets the support they deserve by reading it there.

  The Aud had half detached a hooked claw from the stone when the sonic round hit. The rocky face in front of it smashed into a thousand tiny pieces. A dozen cracks spiderwebbed out from the impact site. They ran up and down the wall in every direction in a blitz.

  The Aud growled, already tracing the round's trajectory back to its source. Her blood ran cold when its head jerked her way. Eyes that made her freeze up latcheted on her in the darkness. But it was too late to do anything. Before it could leap at her to take her head off, its limbs broke free from their holds.

  Only its front legs stayed in the stone, but it was breaking away faster and faster. An Aud's weight was without peer. Gravity dragged it further, no matter how much it struggled to climb back up. Back up to her.

  Rather, each movement only worsened its situation until it scraped an outcropping edge. With murder in its eyes, it captivated her gaze until it disappeared beyond her optics' range.

  She stared after it, ignoring the tremors of her body. What would it take to stop those damn monsters for good? When she resumed the climb, she had to trust the WAV's servos to keep her descent controlled. It'd be a few hours at best before the green climbed back up. She needed to be long gone by then.

  The climb proceeded faster than before. The HUD, as aware of the time bomb ticking above its pilot's head, rerouted the path. Several neon outlines vanished along the climb, and the remaining ones were riskier. Grabbing them emphasized speed and efficiency of movement at the cost of safety.

  After the two-kilometer mark, she had to find a perch to rest. Thank goodness the WAV did most of the heavy lifting using hydraulics and movement sensors. Even then, several drugs her suit carried enhanced adrenaline production for a reason.

  She still had to act as a model for the suit to sync its actions alongside. Which meant every time she grasped, it grasped. Every time it reached for footholds, she painfully stretched her body to make it happen.

  The HUD located a small alcove carved into the side of the wall. It was man-made. Between where she'd found it and how abnormally smooth it was on the inside, she could tell that little. Under different circumstances, she might've avoided the unknown variable.

  As she led the WAV into a sitting position, she couldn't care less about potential dangers. Gratefulness that it was there at all overpowered everything. Curiosity, and by extension, caution, were for another time and another person.

  She panted into the darkness. In passing echoes she heard both the sounds of the cave drafts and the Aud somewhere below. Or around her. 'Please not around me yet.'

  She was sure more were moving along the walls; she had yet to meet them. Light was more dangerous now that she'd already announced her approximate location with her sonic. Not that checking for them that way had magically grown less fraught in recent minutes.

  She allowed the WAV's knuckles to scrape across the alcove floor absent-mindedly. The frown came fast when they raised and lowered in a pattern. Although the suit core was uncomfortably low, she could spare a little power.

  Her night vision activated again, and the optics pushed the darkness back, up to the alcove's mouth. Looking around, she smiled to herself in pleasant surprise. The first since the fort she'd worn to fool herself into thinking positive thoughts. Those events felt like a lifetime ago.

  She was in the center of a spiraling carving, with waves moving up and down in a hyperbolic display. Those were what she felt. It arrayed into a nonagon. At each corner, a triangle raised from the surface. She winced, seeing one of the triangles crushed. She'd stumbled over something when she first entered, dismissing it as another rock. Her bad.

  Then she looked at the other triangles and changed her mind. All but one had received identical treatment. Relentless stabbing motions'd torn them apart. She recognized it from an Aud's signature stomp. Why spare one of them? No, better question, why damage the stone carvings in the first place?

  She tried to study the damaged triangles, but whichever Aud had gone to town, it'd done a fantastic job. She couldn't even guess the original heights of the triangular prisms. "How old is this place?"

  "Addendum: Cues from target's visual presentation and surface material composition incorporated into study. Estimation: Construction of target space occurred no sooner than eighty-three years."

  She felt inclined to agree. Though the alcove looked smooth to an impossible degree, it still had cracks here and there. From the severity of the weathering, it couldn't've been older than a century, though. That wouldn't fit.

  Sighing, she crouched by the final stone triangle. Although she could have broken it off to take, that felt disrespectful, somehow. She couldn't put her finger on why. Her hand wavered over it.

  The lone survivor depicted a carved hand. It had what looked like moss growing over the skin, and it was cupping water. The liquid pooled over the fingers and vanished from the design's edge. Aside from the moss, the hand caught her attention first.

  Not only was it the centerpiece, but it was anatomically wrong. There were eight fingers and two thumbs instead of the traditional five-fingered hand. Odd sight. She wanted to scrutinize the rest of the floor carving.

  Her curiosity acted like an unbridled beast, as hard to cage as an Aud. And she needed to sheath it away. Now wasn't the time to ogle one of the few places humanity happened to miss in past explorations.

  Three centuries of occupying the Gaiss Hollow. That much time would encourage any species, but especially humanity, to create new landmarks. More than once, an exploration survey found some shrine or rock carving.

  They were always hidden deep in the greater tunnels. The servicemen had marked the locations, cataloged what details they could, and continued.

  But exploratory surveys had traversed this greater tunnel dozens of times. Something this high up could be likely to escape notice, but consecutively? Back to back to back? She doubted it.

  The Aud found it. They weren't held back by the same constraints humans were. They had unlimited freedom of movement in every way except flight, and that was a thin comfort. Hundreds of them climbing to the Gaiss Hollow's ceiling and dropping on Io would make a fine case study. Pa-5 winced at that thought.

  And how the other triangular…what? Symbols? Talismans? The others got ruined in a fashion that all but screamed intent. And intent required intelligence.

  Her blood ran cold. Intelligence? No, no, no. No, that couldn't be right. This had to be a simple case of some careless Aud making a resting place decades ago and ruining the art. Without damaging the delicate spiraling patterns on the floor. Or leaving signs of its entry or exit from the alcove. Or--damnit. That wasn't working.

  But why were the triangles the only clearly targeted part of the whole? Why wasn't the rest of the stone carving a fractured, unsalvageable mess? Her hand finally seized the base when she made up her mind. She yanked and felt cracks as the rock beneath yielded. The last talisman came free and entered one of her thigh compartments.

  She was shaking, unsure which idea scared her more as she stared off into the darkness. That the Aud had advanced enough mentally to practice vandalism? Or that this intelligence, no matter how limited, had eluded the Directory's notice throughout a centuries-long war? The HUD injected another cocktail to dampen her stress.

  "Notice: Passive sensor scanning detected light to moderate tremors thirty meters to right. Advisory: Move."

  But when the HUD said that, it was time to stuff away these newest concerns in the back of her burdened mind. Her joints still ached as her climb resumed, but her muscles had stopped feeling like they were on fire.

  The grasp of the WAV was as strong as ever. It combined her coordination and guidance with its raw strength to claw a way onward. The suit leaped and jumped from hold to hold on the HUD's path with incredible finesse. Especially so for something in its size class.

  Her rear and side optics worked overtime. Their mounts rotated back and forth in desperate competition with the movement sensors to locate the first Aud.

  She was through the fifth kilometer--and nowhere near halfway done--when the HUD blared. While flinching from it, she felt her WAV growing heavier. Much, much heavier. Before she could blink, she was falling. The suit's fingers passed through the stone without stopping this time.

  That was her third mistake. She never kept an eye on the batteries for the external anti-grav nodes.