Soylent Green is People!

Afton and Anja slowly make their way through the dilapidated hallways of the vault, a green hue infesting the place along with sporadic plantlife that seems to have erupted from the floor, walls, and other weaknesses in the Vault structure.

Obviously, there was more to meet the eye with these plants... Again there wasn't any sunlight to provide sustenance to them, but most importantly, the materials the Vault had been made out of should have made it impossible for roots, vines, and other organic material to break through it.

Vaults were designed to weather nuclear explosions, and yet the plants are easily able to tear it apart seemingly at their whim.

The duo come across another closed door and Afton protects his face with a rag as he opens it, sure enough, another wave of green miasma flows out from it... After thinking about it more closely, the green particles were likely being produced somewhere, Keely and the Dowager mercenary group had both been through here relatively recently.

It when then Afton figured it out, "Ah, that's what's happening... The plants don't act like actual plants, but instead like some sort of fungus... That'd explain their ability to grow without sunlight." he mutters to himself, his wariness rapidly increasing as that'd mean the green miasma were spores.

He'd seen more than a fair share of zombie movies involving fungus, but... If it was indeed infectious, then his earlier inhalation had doomed him already. Afton shakes his head, he'd complete the job, acquire the research for himself, save Keely and Dowager, before trying to fix this problem.

With renewed vigour Afton steps into the next room, finding it completely destroyed as if a hurricane had passed through here. Tables were overturned, machinery was infested with roots, and the lights occasionally flickered which meant something was likely wrong with its connection or the reactor itself.

The next few rooms looked to be observation areas, with windows peering into restricted sections of the Vault... Clearly their containment efforts had failed considering the plantlife had reached the outside of the Vault already.

Honestly, Afton was surprised to have not found any enemies yet... Perhaps he was wrong and the mantises were the only threat?... Pfft, yeah right!

He continued looking around the area, eventually finding a rucksack filled some grenades and other rations... Probably belonging to either Keely or Dowager, though why they would leave it here beats him.

Walking onwards, he and Anja find some sort of elevator system, of course it's broken and unlikely to be operable for some time... He could try to fix it but that'd probably take a couple of hours, something he was hesitant to attempt due to the likelihood that the fungus would try to infect him in some way.

Shaking his head he heads to the staircase leading to the lower floor called the Oxygen recycling floor. Once through the door, the duo were greeted by a dark hallway, one where the lights had apparently completely malfunctioned.

Using his Pipboy light as a torch, he illuminates the plantlife infested the path ahead, his eyes narrowing when he spots a figure amongst it. He readies That Gun which causes Anja to prepare for combat herself as he tries to speak to the figure, "Hey? I see you there, why're you hiding?" he asks in a clear, but calm tone.

...

Receiving no response he grabs some empty cartridges from his bag and tosses them at the creature, the metal loudly bouncing off of the Vaults metal floor. Both Afton and Anja are startled when a green arm shoots out from the foliage and slams onto the cartridge, slowly dragging the object into the plant life afterwards...

"What the fuck is that" Afton mutters dryly, "Anja, did we fall into a portal to the nightmare dimension or some shit? That's some silent hill, Lovecraft shit right there." he states, gesturing at the hidden monster with his pistol.

Anja doesn't answer, of course, her eyes not leaving the place where the arm had erupted. It seemed that while Afton had an idea about what was in there, Anja did not. She'd never seen the horror movies he had and had no inclination over what to expect. Not that Afton himself was in control of the situation mind you, he just had a vague idea over how this adventure was likely to go.

"Anja, relax, if you start spraying all of your bullets randomly then it won't be the monster we have to worry about." he says, trying to persuade her not to accidentally shot him in the back in a panic. At his words her breathing slows somewhat in the manner he had taught her.

"Alright, on my mark we'll blow the shit out of that thing hiding there, after that we'll keep an eye out in case the sound attracts anymore" he states before lining up his shot.

*BANG!* *Bang!Bang!Bang!Bang!*

The sound of gunfire echoes throughout the metal hallway, most likely alerting any sentient creatures. During the attack, the hidden creature launches itself out of its hiding place and start rapidly crawling towards the duo on all fours.

It was humanoid but had no eye's, only a huge fang-filled mouth that snapped at them voraciously. That is, until their bullets rendered it nothing but a pile of green flesh.

It stopped moving after a bullet penetrated its skull, but the duo wasn't willing to risk being sneak attacked by it. Not to mention the fact that more could be coming at any moment. They just stayed at the end of the hallway, waiting for the rest to arrive...

...

After a couple minutes of waiting, it appeared that either the creature didn't care about the sound, or merely didn't hear it... There could be other reasons however, ones that Afton hoped weren't true... For example, the fungus being a hivemind organism like the Flood from Halo, or Necramorphs from Deadspace... Truly, if the fungus operated anything like those two 'fictional' plagues then he, as well as the rest of the world was truly fucked.