There was a grate mounted to what looked like an air duct, but had a much thicker outer wall. The grate was torn open, claws had ripped the metal apart like wet paper.

Heller remembered being shredded by those talons as well, and still was already halfway diving into the opening when Mercer's steel-like grip stopped him dead in his tracks.

"You really think this is a good idea? The last time you went after one of these things it didn't go over so well."

Heller snorted. "Yeah, well now I know how to deal with these things, so its acid blood won't be taking me by surprise."

Mercer scoffed "Famous last words", though let go of his arm. "I'm going in with you."

"You? I remember you hated tight enclosed spaces."

"I hate having to chase after you to resurrect your stupid ass much more. So." He slipped past him. "Let's see where this thing went."

Heller shook his head, but followed after the Runner. "Did I mention that those things don't have an own scent?"

"You did. But also, this maintenance tunnel hadn't seen any maintenance for a while, so there's enough dust to follow its tracks." Huh. He was right about that one. Okay, one for the smart-ass.
Though, he suspected, he didn't get to have all those really fancy tricks since Blacklight didn't actually operate like organics should work, and those tricks just didn't translate too well when applied to his body.

So he shut up and focused on following his superior through the tunnels. They were narrow, barely enough for him to stretch both arms and certainly too low to allow him to walk upright, so this crouch-walk he was currently doing was Hell on his knees.

The maintenance tunnel suddenly dropped in a ninety-degree angle straight downwards, with only a fragile-looking ladder there for mounting. Everything was dyed in harsh red security lights, making the ladder look even more derelict than it probably deserved. Still, he was glad he wouldn't need to trust it with his life when he followed Mercer's lead. Of course, he did the sensible thing and slid down by bracing his limbs against the walls. Mercer just hooked his claws into the walls and scrambled downwards head-first, obviously searching for the track.

Halfway down the shaft he paused, motioning downwards. Heller caught the glimpse of a black tail vanishing around a bend, and nodded grimly. Both Infected let go of their perch and dropped down, catching themselves just shy of the ground to prevent cratering or breaking through the floor.

The thing was already gone. Mercer curled his nose. It's fast.

Heller scoffed. Hivemind of course, to avoid being overheard. "Impressive, given these narrow-ass tunnels."

It's adapted to living in such habitats, then?

"Possible. Would explain the sewers."

Mercer nodded, and continued leading the way. Heller figured that they were currently above the production floor, because the maintenance walkway opened up into grates in regular intervals, allowing to look into the offices and labs at floor-level. He found himself baffled when he spied the construction plans for what seemed to be an APC, and one for a V-TOL like plane.

"Wonder who designed this place" Heller mused. "Hell, I can see plans from here. Do they want their shit to be stolen?"

I can only assume that they want to. Mercer replied. Or, given that the CEO is likely handing out working prototypes to the Bears, they figured they don't need any security against corporate espionage. His lips quirked up in a small smirk. After all, who wouldn't protect their goose laying golden eggs?

Yeah. Got that one right. It was just... "What is that thing doing here then?" Animals usually didn't do corporate espionage.

Mercer shrugged. Either its handler can see through them and uses them to spy on companies, or, the handler is here somewhere, or its presence is pure coincidence.

Heller scoffed. "Riiight. Then what about the Bears shooting up my ass and/or stealing evidence?"

Maybe they owe the handler one, or they are one of them. Mercer shrugged again and continued moving. One way to find out, no?

The crawlspace changed its direction a few times, until it suddenly ended in a steep drop. Far deeper than the one they already encountered, and far larger. Elevator shaft, Heller corrected himself when one cabin slid past them and vanished in the dark below. Mercer only cocked an eyebrow, squinting. Dozens of openings. It could be everywhere.

Heller craned his neck to glance down, too. "Try the bottom first. Bad guys either hide down below, or far above everybody else."

Mercer smirked, and lunged out of the maintenance hatch to let gravity get a hold of him. Heller leapt after him without hesitation, though he was more mindful to get his feet below his body as soon as possible, not like the Runner who seemed to remember that people usually didn't land with their faces like two seconds before the final impact.

The force shook the elevator shaft, but if there was one thing Heller had long since realized was that people just. Don't. Care.

Down here, he figured it was safe to talk. He knew Blacklight thought different, but the Hivemind always hurt his brain. "Where to now?"

"Honestly? No idea", Mercer admitted. "This thing could be anywhere. Though..." He glanced back upwards. "Pretty deep down, don't you think?"

"Yeah. Too deep to be archives, or something."

Mercer grimaced briefly, and Heller had a very short mental flash of memories. Memories of a laboratory deep underground, with freezing air.

"Got it", the Evolved grunted. "Bad shit happened. Let's go take a look around." He stopped however, eyes narrowing. "Smells like burnt metal, don't it?"

"Acid burn", Mercer confirmed with equally narrow eyes. "Old. Stale."

"Let's check it out", Heller decided, already pushing to the front. There was another opening at the bottom of the elevator shaft, and it opened into a form of network running below the floor level of additional rooms. He suspected it was some form of air circulation, or maybe a heating system, since the air was pretty bad. Probably was just because Blacklight was pretty hardy that neither of them hadn't reeled over from acute Carbon Dioxide poisoning yet (though, to be fair, Mercer didn't actually need to breathe, so it was probably lucky for Heller alone).

He already got used to the dim light around him (possibly with the aid of Infrared), so he noticed a dried-up spot on the floor very quickly. It looked a lot like the acid damage on Moore's examination table had looked, but was much bigger. A grate was above them, also partially eaten through, and easily broken out of its mounting. Was nobody around to hear them, though, so Heller pushed the obstacle across the floor where it ended in a corner. Mercer fluidly climbed into the room first, followed closely by the Evolved.

There was one of these things on the table. Long dead by the looks of it, and thoroughly gutted. Not the one they had been following, then.

Mercer scanned the thing in that creepy unblinking way he always did. "That the one that attacked you?"

Ah, so that was the angle. Heller too took a good look, and his brows drew together. "It's not. Mine was brown. This one's black."

More differences, the longer he looked at it. The domed head was ridged, not smooth. Its hind legs were less bent than at the one he fought. It had tube-like spikes along its shoulders. "Mine was four-legged. Like a cat. This one..."

"Bipedal. Like a person", Mercer finished. "Hip structure seems to indicate an upright position."

"So there's different types then?" Heller furrowed his brows deeper. "There had been many missing pet reports. And the thing I fought...could have looked like a dog or cat, honestly. And-" He grimaced briefly. "Who says these things only parasite humans?"

The Runner stilled. "You're meaning to say that these things hatch differently, depending on the host?"

"Is that possible?"

"Yes. Through horizontal gene transfer", Mercer muttered. "Most bacteria can swap out pieces of their DNA with other bacteria of the same species. Some bacteria seem to transfer their own DNA into host beetles, which allows them to digest food more efficiently." He cocked his head, smirking. "Some viruses mutate differently depending on their hosts."

"Ah shit", Heller ran his hand down his face. "Parasites are already bad enough-"

"Parasitoids", Mercer corrected absent-mindedly. "Parasites usually don't survive without a host. Parasitoids kill theirs to grow."

"-But stealing their host's DNA is something else entirely", the Sergeant finished as if he hadn't been interrupted. "Fuck, what do they do with it?"

"Best guess? Adapt." Mercer hummed briefly, glanced at the still-closed door, before he went to switch on the harsh examination lamp. Heller swore for a bit, but by the time he could see anything other than stars, Mercer was already beginning to examine the dead creature.

Its hide was glossy black, looking as if somebody carved chitin into a skeleton. The joints were covered with thin skin, equally black, and pretty resistant itself. It had six fingers, with two pair fused to each other, and four toes. All of them clawed. Metallic teeth, sharp-edged but otherwise blunt, like chisels. Canines pointed. Jaws long, and partially connected to the upper jaw with tissue.

The Runner whistled, drawing attention. "Look at that" He grabbed the thing's throat and twisted slightly, and a secondary jaw suddenly thrust out of the thing's mouth. Mercer grinned gleefully. "A pharyngeal jaw. Like a moray eel."

Heller hissed through his teeth. "You seen the kind of power it had coming out? Bet it could punch through a skull with no trouble."

"Probably. Best to keep your distance from it, looks like it can add at least ten inches to its reach."

The older snorted. "Already figured I'd keep my distance. Punching a thing that explodes into acid is not a good idea."

Mercer seemed thoughtful. "Strange about that acid blood", he muttered. Then turned his attention to the already cut-open thorax area. "No other liquids. This stuff is not only beneath the skin. It is its blood. But..." He trailed off, glancing at the acid damage at his feet. Then he shook his head, muttering later, before returning his attention to the thing's organs. From what he could see, Heller had to realize that they didn't look like anything he knew. Mostly tubes and glands, all coated with dense muscle. He did however recognize its lungs and its heart and even its brain, exposed from the earlier necropsy.

Mercer abandoned its torso for now, picking up its head, before roughly yanking it off with a bone-chilling crack.

Heller winced, eyes instantly snapping to the closed doors. If those guys hadn't noticed them dropping into their elevator shaft and breaking out the grate here, then they would still probably realize their little excursion when they discovered the cadaver being mutilated. The Runner didn't care much, however, just turned the head in his hands and squinting at the smooth front. "No eyes. I think those could be ear openings, but..." He furrowed his brows, then shifted his free hand to his claws to cut into the thing's forehead, peeling off the black layer with a sickening squelch.

Heller hissed through his teeth. The back of the skull was elongated, with ridges vanishing under the armor, but the front seemed to be startlingly human. Empty eye sockets stared at them. Mercer tilted his head. "Still no visual systems. How do you see?"

The other cleared his throat. "Maybe it doesn't? Maybe it's a tactile-based orientation?"

"Mhm. Maybe." The Runner turned the head around in his hands before putting it down and going back to the torso organs, sifting through them with renewed vigor. Heller knew he wouldn't be much of a help here, so he kept his senses peeled to listen to the other side of the door. It helped to focus instead of mulling over the question what he was going to do if somebody actually stepped through here- things like that kept happening to him because he literally jumped first and only asked questions once he finished blending whatever he met at the bottom.

Then Mercer made a disgruntled sound, drawing attention, though the Evolved didn't take his eyes off the door. "Acid trap?"

"Worse", the Runner growled. Okay, that got his full attention. Heller twisted his head around to look at the younger, who had obviously finished disemboweling the cadaver and was now glaring at the hollow space below its ribs. He shifted then, glaring at him from the corner of too-narrow too pale eyes. "What do you think this is?"

Heller followed the gaze, finding nothing worth mentioning when looking at the thoroughly gutted carcass. There were still some tubes, some glands, muscles, tissues- "Hold up", he growled. Then pointed at a mass at the lower bottom of the body. "Are those what I think they are?"

Mercer nodded grimly. "Ovaries. It's female."

"And females give birth to more of these things. The spiders."

The Runner growled low in his throat. "Likely, but we don't know enough about their biology."

"Yeah, but alone the fact there are females means we have to pick up our feet. Because it could mean a breeding population. And if that is true..."

"Then they won't even need a conduit creating them", Mercer finished his thoughts. He scowled briefly. "We could be looking at a biological weapon here."

Heller scoffed. "We should call Cross. Get Blackwatch in here."

"We should", Mercer agreed. "However, we don't have enough information as of now, and if Blackwatch rolls in here without us knowing what we're dealing with, we could fuck things up even worse than they are now."

And shit, he was right about that one. If these things reproduced by hatching from living hosts, then bringing in more bodies just asked for misery. "We have to figure out where they come from", he realized. "Take out their nesting grounds. Make it safe for troops to go in."

Mercer lifted a finger. "We need to find those nesting grounds first, however."

"You think they are here?" Heller glanced around, trying to imagine the endless hallways beyond those walls.

"I'm not sure", the younger frowned, staring at the door himself. "I don't think so. But something is here. The Bears know it."

"So. Go out and eat some of them."

"Later", Mercer went to the door, opening it slightly to peek outside before sliding it aside and passing through. "First, let's see whether we can't find any information about what is going on here." His lips peeled away in a wide grin. "And figure out what these guys learnt about those things. Maybe they found a way to work around the acid blood that doesn't involve it bleeding out for a few days."

The hallways beyond the doorway were only wide enough to allow two men walk side-by-side, with a ceiling made of thick grate just a few feet above their heads. The very second both heard people approach, they slid into the fake ceiling through a small opening off to the side.

Three security guards walked past them without even realizing their presence. Mercer watched them pass by, before he soundlessly slid back through the narrow gap to land behind them and close in on his prey-

Wait.

He stopped all movement and cocked his head over his shoulder, eyes narrowing. Then, just as soundlessly, he climbed back into the fake ceiling, leaving the three security officers alone without any of them knowing how close he'd been. Heller grit his teeth, rounding up on him. "I thought you wanted to have a snack?"

The Runner seemed absent. Sh. Listen.

Heller's jaw snapped shut with a click, and he strained to pick up sounds- His eyes widened slightly. "Claws. Metal breaking."

It's around here somewhere.

Mercer instantly scampered off into a seemingly random direction with Heller close on his heels. The younger stopped at the end of the hallway to quickly pry another grate off the wall there. The narrow vent opened into a roughly triangular room with a hatch and ladder to the side. Mercer made a straight line for it, though ignored the rungs and casually lunged upwards.

By the time Heller caught up to him he wrenched another door open. He noticed the 'Restricted Access' signs next to the hinges, and his heart skipped a little. "This looks promising"

The Runner only nodded, and easily pulled the obstacle open to reveal another hallway. There was only one other door at the opposite end of it, and Mercer made a straight line for it, stopping in front of what was definitely a scanner.

Heller whistled. "Iris and Hand-print scan, and a card reader. Somebody definitely doesn't want visitors."

The other just grunted in reply, then checked the cables connecting to the device. "I bet you trying to force this thing is going to cause a silent alarm."

"No bet. Shit's definitely wired."

The younger sighed. "Locks like that I can't open. A code is one thing, but first off, we don't know who got the code, and second, I won't be getting through a print scan either way." His arms rippled and twisted into his claws. "Which only leaves option three."

Heller shrugged. "Break shit, take whatever looks important, and get out before the security gets a glimpse of your face." He paused briefly, then added as afterthought "Or silence the security."

Mercer's teeth shone in the darkness. "I love option three." Then he jabbed his talons into the door frame and ripped it open. Heller half-expected a wailing alarm to follow, but everything remained silent except for a sharp hiss uttered by the Runner.

Which was an alarm all in itself, and Heller instantly followed the younger's line of sight. There was a reinforced observation window across from them, and beyond that- Heller hissed. "Fuck"

It was like staring at Manhattan's skyscrapers, with flesh and tendrils attached to the surface inside a large room.

The only difference was, it was in blue and black, not red and orange. Also, the deformed infected were missing, replaced by dozens of sleek black and brown creatures clad in skeleton-like armor.

"The brown guys are like the one that attacked you, right?" Mercer questioned simply.

Heller nodded. Narrowed his eyes. "You were right on the money. Black guys are two-legged, brown guys four-legged."

"Different skulls, too", the Runner pointed out as he continued to observe the things. Heller admitted he was correct, too- the brown ones had a more narrow and longer face than the black ones. Obviously dog-like.
Different crowns and back of the heads too, the longer he looked. There were smooth skulls, ridged skulls, and he even saw what seemed to be the beginning of a crest. Since both versions showed those, it was possibly something that had to do with age, or maybe a different caste within the swarm.

None of the things were moving however, just sitting hunched over in random places all over the area, only twitching from time to time. They were constantly drooling too, thick saliva dripping from their teeth and plopping to the ground after a while.

"Think this is where they come from?" Heller questioned.

Mercer cocked his head. "Seems like it, no?" Then he frowned. "But. Where are these spiders?"

"Different pen, maybe?"

"Maybe" The Runner turned his attention to the side opposite of the observation window, eyes gleaming. "Surveillance gear. Computers. Was to be expected, but still. Jackpot."

Heller's attention was off him and on the booted feet stomping towards them. "Gotta hurry. Security's coming."

Mercer didn't even lift his head. "They're fast."

"Yup"

There was a series of cracks, and when Heller turned to glance at the younger, he had already finished gutting the computers. "But I'm fast too"

"Yeah, just get moving-" He cut himself off at the sight of movement from the corner of his eye. Reflection maybe?

No. Second observation window. Something moving behind it, black and sleek. Claws shining in the low light, second before a bright flash.

The alarm started blaring, and all the animals in the pen suddenly snapped their heads up the very second something shut down. Like on signal, all of them suddenly surged towards the walls, mounting them just as easily as if they were running on even ground, before slipping through a hatch in the ceiling one by one.

"Fuck"

Mercer grimaced. "Same here." He grabbed the computer's motherboards and shoved them roughly into his chest. "Think we made a mistake. Think these things don't actually belong here."

"Yeah, think so too." The steps outside had stopped just as the alarm started and were now retreating again, the guards swearing at the top of their lungs. "Good news though, way's free now."

"They'll be probably distracted anyways", Mercer rushed to the front and yanked the door right out of its hinges, slipping outside without slowing down much.

Heller was close on his tail when the younger dropped down the ladder and hurried back to the autopsy room with the mangled carcass. "What about-?"

"Those things? At the moment, we can't do much", the Runner pointed out when he slid into the cramped ventilation system. "We need to find out what they learnt about them, or we'll get some really big guns and loads of ammunition. I don't see any other chance at how to destroy them."

"So...you're just going to leave it at that?" They scaled the elevator shaft now, avoiding the lift cars almost as an afterthought.

"For now. But if these guys lock this place down they'll likely search it from top to bottom, and I don't want to be anywhere near it should they decide to activate a scorched earth protocol."

Good point. Plus, it would probably be hard to explain what a NCIS agent was doing in a highly restricted area.

Once we're out of here, we'll need to check the computer drives, Mercer pointed out when they returned into the maintenance shaft. The labs still looked the same, but the scientists were running around like headless chicken, and security guards were swarming the place.

Heller nodded grimly. "You do that. Find me whoever runs this place. Let's see whether Hetty doesn't get me a warrant so I can have a little chat with him."

Mercer stopped, frowning. On what reasons?

"No idea yet. I'll come up with something."

The Runner snorted, and slipped out of the opening at the roof first. When Heller caught up to him, he was watching the courtyard below. Nothing had changed up here. No panic, no guards running around. No Alarm.

Not one of those things up here. Heller frowned. "Guess this place has an own connection to the sewers, and that's where these things are now."

"Likely. But trying to hunt them down there...not a good idea. At least unless we learn more about them."

Heller furrowed his brows deeper. "I would suggest using a Devastator, but I don't think you'll find any group large enough of these things that'll make it efficient."

"Plus I'd be burning myself off. And get a full-body acid bath. Not my idea of a good time."

They fell silent, checked the area below for a long moment, before both lunged off the roof to vanish between the trees nearby.
"Okay. I've been thinking about that acid", the Evolved pointed out once they got some distance between themselves and the compound. "It loses its acidity pretty fast when making contact with air, and turns into some kinda slush. Right?"

"It appears that way."

"Right. Did you find any hint of this thing having another circulatory fluid?"

"Nope", Mercer was grinning now, which meant, yeah, he was on the right track.

"So, how in the Hell does this stuff act as oxygen transport if it curdles when in contact with air?"

The Runner's grin widened. "Remember what happened when you injured one?"

Heller suddenly stopped, eyes narrow. "That shit sprays everywhere."

"Exactly. I think both are connected."

The Heller's eyebrows shot upwards. "It's pressurized, you say?"

"Most likely. High pressure might alter its chemical makeup enough so it actually works as blood." His grin turned sharp. "And that might just be what we need." He didn't elaborate on that one, Heller could already guess.

And it made his stomach churn unpleasantly. If Mercer noticed, he didn't show, but he did notice the way the older of both dug in his feet and squared his shoulders. He only arched an eyebrow under his hood. "Get moving. I'd like to check out the stuff we found."

"To figure out who to throw under the bus. Right?"

The Runner tilted his head. The expression on his face said he knew exactly what the Evolved was talking about, but Heller felt it needed to be spoken out loud. "You want to find somebody in those files you can use to lure in one of these spider things close, don't you?"

The grin he got in return was razor sharp like broken glass. "The adults are too much trouble to try to consume, and the spiders are likely to die off, so I'll need the intermediate stage. The infant stage."

"The stage that chews out of a man's chest."

"Yeah. Well, I'd like to get this done before it matures completely and kills the host. No need wasting good Biomass."

And there it was. Heller didn't have any way to react to what was a perfectly viable line of thought planned out by an inhumane and highly efficient organism. And he had no chance trying to create some sort of morality in a walking virus either. He wasn't sure whether he wanted to, either.

Because everybody who was going to appear in those files was somebody who knew about a terrifying parasite that literally ate its way out of a human's chest, and didn't give a single shit about it. More even, alone the fact that the Bears seemingly tried to cover it up told him that these guys were doing something with those parasites. He could hazard a guess and was willing to bet money if it wasn't such a sucker bet.

Because the only logical conclusion he had that formed out of the pieces he had- deaths being covered up, observation pens, captive creatures, extensive files- was clearly Bioweapon Research.

It was ideal. These things reproduced by killing humans, grew fast, and were smart. With a little training they could be aimed at basically any opposing force and let loose, without their handlers risking being uncovered. Handlers Heller wanted to get dead to prevent them from unleashing a horror that could very well threaten the entirety of mankind.

And Mercer was going to make them dead. Simple as that. It was horribly easy, it was the best choice, and it was fucking terrifying. He'd always been a good soldier, always believed in doing the right thing- but this entire situation just sat wrong in his stomach. The best way to stop this in a timely manner was to literally expose somebody to a parasite that ate its way out of people's chests.

Heller grit his teeth. "Make sure you get somebody who fucking deserves it."

Mercer's expression was still that unhinged grin. "Don't worry. I will make sure. Hell, I even let you pick a target if it makes you feel better. Just pull the trigger, put down a terrorist. Simply the same things you've done when you were still with the Marines." Then he sobered up, and stopped at the edge of the Asheville military compound. "Besides", and he gestured to the Blackwatch helicopter parked at the Airfield, "I'd rather not make dad angrier than he probably already is."

Enter Blackwatch.

Also, this chapter contains heavy headcanon I made up regarding the Xenomorph species- especially the gender thing. In my opinion, there are no males of the species, only females. Any drone can grow into a Queen, which makes them even more dangerous.
Additionally, they change their appearance based on their hosts, so I don't think that their heads look the same when they hatched from people or dogs.

The more you know.