As mentioned in the description, this is based on some unused sound clips in Portal 2's files. In them Wheatley talks about an area called the "Neurotoxin Control Room" which as a "Neurotoxin Release Button" in it, and how he, well I won't spoil the story ahead. But its' based off those quotes.

Bring Your Daughter to Work Day

Aperture Science was used to having failures, it is part of the road to progress after all, however they had never failed quite as spectacularly as they did with the intelligence dampening sphere. Created to make GLaDOS too dumb to continue her daily attempts at murdering the entirety of the company, it instead caused the computer system to try and kill them just as much as normal but with really stupid and poorly though out plans. Usually these ended up damaging GLaDOS herself and causing billions in property damage. When the costs became too great the sphere was finally removed and given a multitude of odd jobs around the enrichment center.

'Wheatley' as his programmers affectionately called him, or as affectionately as people who created said personality core to be a moron and regularly reminded him of it could be, was most recently given the job of watching over the employee daycare. It was theorized that his bumbling antics and pleasant British voice would endear the children to him and keep them behaving. The scientists were wrong, of course.

When the scientists came to pick up their children at the end of Wheatley's first day of working there they found absolute chaos. Drawing tables were overturned, baking soda volcanoes had erupted over the walls, and Wheatley had been pulled off his management rail by a particularly strong child and was now being used in a game of kickball. Wheatley was in tears, or as close as robotic eyeball can come to that, and never returned to said daycare center. The scientists also made sure to tell Wheatley if he ever disengaged from his management rail again he would die.

After a few weeks of wondering what exactly to do with Wheatley, who had resigned himself to wandering around the facility, babbling inanely, and accidentally insulting most of the people who bothered to listen to him, Aperture Science came up with the perfect role for their moron. A job so simple, not even he could mess up...

The most recent attempt to control GLaDOS was quite a simple one, remove her control over the neurotoxin generators. Instead an area known as the 'Neurotoxin Control Room' was built. It was a cubic, mostly featureless room, containing only a tinted window looking out to one of the office areas, and a podium with a button on it, the Aperture Science Neurotoxin Release Button. If pressed it would allow GLaDOS control absolute control over the generators, and as a deterrent to those who might wish to help the AI, it would first flood the entire enrichment center with deadly neurotoxin.

Due to the immense danger to the enrichment center that being flooded with deadly neurotoxin would be, someone would have to monitor the button 24/7. It was the simple job that not even a moron could mess up, and was thus the aforementioned plan by the scientists to occupy Wheatley. He was put in charge of making sure the Neurotoxin Release Button was never pressed. For several weeks everything went swimmingly. GLaDOS' attempts to kill everyone were at an all time low, and Wheatley was at last out of the staff's hair.

With things safe, or as safe as a company that had orders to capture OSHA workers on site and wipe their memories, then use them as test subjects could be, Aperture Science could hold their annual Bring Your Daughter to Work Day celebration. There would be a tour of the enrichment center, a science project contest, even a test chamber specifically designed for the little ones to get the world's first glimpse at the handheld portal device. It would be the kind of day that would boost employee happiness above the negatives, a difficult feat since they had made employee testing mandatory.

The girls were all setting up their science projects, virtually all of them potato batteries. There was the odd baking soda volcano, and one flux capacitor, but otherwise the competition wreaked of sameness. One black haired eight-year-old's project however, was about to become very unique. On the way to the enrichment center she had covertly swiped a vial labeled 'growth-serum' out of her father's lab coat, her trump card. The girl uncorked the test tube and poured its contents over the potato battery, which immediately began to grow. Roots sprouted from its top and climbed near the ceiling to assure her victory. The young girl did not like losing; a test, a competition, not anything. She was tenacious like that.

While the other girls looked in horror the girl calmly wrote "By Chell" onto the project's accompanying poster board and wandered off to explore. The enrichment center's design was rather haphazard, a result of building it to accommodate constantly rearranging test chambers. To make space some sacrifices in design choice had to be made, such as squeezing the employee daycare center and Bring Your Daughter to Work Day location right next to the neurotoxin facility.

Needless to say, Chell managed to find her way into the Neurotoxin Control Room within minutes. She glanced around and upon deciding that no one else was there, she slammed the door shut. The loud noise however startled the strange orb thing that had been hanging from the ceiling. Chell jumped back in shock as it turned to face her, having previously believed it to be nothing more than a light or security camera.

"What the bloody hell are you doing back here?" Wheatley narrowed his optic at the intruder. "Do you have any idea how much trouble I'll be in if management finds out I let a human into the neurotoxin release room?" Chell stared blankly at the strange robot eye thing that was scolding her. Wheatley could not exactly place it, but he was sure he had seen this little human before.

"Oh, you're one of the kids from the daycare aren't you? The one who would never talk. What was your name again? Don't tell me, don't tell me." Wheatley scoured his memory banks. "Oh yeah, Chell. Doug's kid, right?" Chell either could not or refused to answer. "Because you don't really look like him. Were you adopted by any chance?" When Chell once more withheld any answer Wheatley remembered he was supposed to be making sure humans like Chell were not in the control room.

"Alright, this' been a good talk Chell. But you need to go. Now." Chell crossed her arms over her chest and glared at Wheatley, she was not going to let a weird eyeball-thing tell her what to do.

"Seriously, get out now, this place is bloody dangerous. See that button there, luv? That's the Neurotoxin Release Button, if anyone pressed it, like so," Wheatley lowered himself down until his chassis was resting atop the button then quickly drew back up. "It would flood the whole enrichment center with deadly neurotoxin."

Neurotoxin release activated, you now have approximately five minutes to live. Aperture Science apologizes profusely for any inconvenience this may cause. An automated voice announced cheerfully over loudspeakers throughout the facility. Wheatley's pixilated pupil widened to cover his entire optic. "No! Nonononononononono! That didn't count, I was just demonstrating to her!" Wheatley began to pant heavily, a feat Chell thought pretty impressive for a being without any sort of respiratory system.

"Calm down Wheatley, calm down. Everything's gonna' be alright mate. Just, let's see. Maybe if I press the button again?" Wheatley almost accidentally disengaged himself from the rail in his haste to lower onto the button. Neurotoxin release rate doubled, you now have approximately two-point-five minutes to live. "Argh! I am so fired." Chell looked around nervously, but noticed that while through the window a green mist seemed to be covering the center, the neurotoxin release room was safe.

"Oh yeah, the neurotoxin won't flood this room, so you're fine. Hmm... Maybe it just wants to make sure you really want to stop neurotoxin and have to press it uh, five times?" Wheatley slammed his spherical body onto the button several more times. Neurotoxin has been fully released. If you can still hear this message, congratulations, you're immune to deadly neurotoxin. Please proceed to the Aperture Science Surgery Station so we can dissect you and learn the cause of your immunity.

Wheatley and Chell both glanced out through the window and were greeted by a sea of green mist with several slumped over figures within. "Well, on the off-chance that anyone survived, we should probably get our stories straight. Now what do girl-humans like? Uh, okay, you saw... a pony... and it was so... amazing and pony-ish that you were distracted... and didn't see who pushed the button. For all you know it just malfunctioned. Yeah, nobody pushed the button, it just... pushed itself! And... I was in the break room, on break... making sure nobody there was planning to go push the button... oh who am I kidding." Wheatley hung limply from his rail.

"I am so fired, and need this job. I've got a wife and three replicas to feed!" Chell raised her eyebrow at that particular outburst. "Okay, I don't. I was just being dramatic. But, there is this nanobot down in accounting I've chatting up. Got her recharging bay number last week, I think she entered it wrong though 'cause it lead to a turret redemption line." Wheatley sighed while Chell wondered how he did that without a mouth or lungs. "She's never gonna' talk to me again after this. If the scientists don't kill me first."

Paranoid schizophrenia has its benefits, Doug Rattmann thought as he double checked the straps on his gasmask. He had kept one stored in his locker just in case of such an occasion. Tucked under his arm was the morality core, likely the only thing that could remove the neurotoxin from the enrichment center. He didn't know how GLaDOS has circumvented the release button, but that was a problem to deal with later, right now he had to get that core installed in GLaDOS before it was too late.

Through the haze of deadly neurotoxin Doug made out the shape of GLaDOS' chassis, swaying back and forth as she surveyed her new kingdom. Doug clenched his teeth and sprinted forward.

"Oh, hello there Mr. Rattmann. Someone really needs to get to the bottom of deadly neurotoxin issue. Oh wait, my sensors say that everyone else is already dead! How unfortunate..." GLaDOS did not normally show much emotion, but today the glee in her synthesized voice could hardly be contained. In her joy at having revenge at her creators and captors, GLaDOS paid little attention to Rattmann. It was only as she felt the morality core booting up inside her did she realize what was going on. "Oh you little-"

New core detected, warning: new core contains auxiliary functions and requires a system reboot. GLaDOS' yellow optic darkened and her chassis went limp. Doug watched as the neurotoxin mist began to thin now that the morality core's system reboot had stopped the deadly gas's flow. He tentatively pulled his gasmask off and ran. GLaDOS would be back online within minutes, and even without her neurotoxin he did not want to be in the same room as the AI. Rattmann had been planning for this day months in advance, he had picked out several test chambers with malfunctioning panels that could lead to safe hideouts until he found another way out. There was no doubt GLaDOS would have already locked all the conventional exists once the neurotoxin started flooding in.

"If they don't kill me, they'll probably give me some awful job like public relations. You know, one of the scientists told me there used be to be a guy who worked public relations who, get this, was also named Wheatley. Said he vanished right about the time I was built, pretty weird eh?" Chell was sitting on floor with her arms around her knees. The reality of what had just happened sunk in, everyone in the facility, including her father, was probably dead. She'd already lost one father, it was no secret that Chell was adopted, and she couldn't bear the idea of having lost another. Tears began to well up in her eyes at the thought, but she tried not to let the eyeball thing see. Unfortunately he did.

"What's wrong? Oh yeah, the others humans... Listen we'll be fine. Everything's gonna' be alright. Little old Wheatley will fix everything. You'll be back out doing uh... whatever girl-humans do, in no time." Chell smiled a bit at Wheatley's attempt to cheer her up. They obviously weren't going to be fine. Her dad was most likely dead, and Wheatley would probably get thrown into an incinerator for this, but it was the thought that counts.

Chell's eyes widened and she ran up to the window. Outside the green fog of neurotoxin had vanished. Wheatley followed her gaze and came to the same realization. "Hey, the neurotoxin's gone! Come on Chell, let's get out of here! But stand back, first I'm gonna' have to hack the door open." Chell simply grabbed the door's handled and pushed it open. "Oh, it was unlocked... I knew that." The exited the control room and stepped into the now eerily desolate hallways of Aperture Science.

A small security camera swiveled towards them, then focused on Chell. "Where did you come from?" GLaDOS' freshly rebooted voice rang out over the intercom. "Never mind. I'm in need of some new test subjects. A 'massive tragedy' can't get in the way of science after all." A section of the ceiling slid away and robotic claw descended from its place. The claw grabbed Chell by the back of her shirt and began to lift the young girl up.

"Hey! Leave her alone!" Wheatley growled towards the claw.

"And you must be the moron who flooded the enrichment center with deadly neurotoxin. Thank you." GLaDOS had did something none of the scientists had, given Wheatley a compliment. This surprise momentarily distracted him, enough for GLaDOS to finish hauling Chell up into the ceiling.

"It was nothing really..." The claw descended back down and grabbed Wheatley. "Um, what're you doing?"

"Giving you your reward." The floor beneath Wheatley fell away to reveal a deep descent into one of Aperture's production lines. GLaDOS' claw ripped Wheatley from his management rail and unceremoniously dropped him into the newly formed hole. Wheatley screamed about how getting pulled off his rail would kill him all the way down.

999999 later...

Against all odds (at least what he believed were odds), Wheatley had survived being disengaged. With the help of a nanobot work crew he'd gotten back on his rail and settled into life serving various odd jobs, making sure to stay out of GLaDOS' eye lest he get killed. The nanobots who had taken over managing Aperture's infrastructure put him in charge of watching over the test subjects within the extended relaxation annex. Wheatley wasn't quite fond of looking after a bunch of smelly humans, but at least it was far away from Her and thus unlikely to get him killed.

But now everyone was dead. Management had forgotten to tell him how exactly to take care of the sleeping test subjects and even worse, the facility was falling apart. Wheatley had decided that it was high-time he escaped, but to do that he'd need a partner. Someone who could use a portal gun and open doors and listen to his amazing plans. He had already found six test subjects that were miraculously still alive, but none of them had been very good at escaping... and had all died.

The most memorable was one named Marissa Roberts who appeared to have been extremely brain damaged from stasis. She ranted on about having the ability to fly out of the enrichment center. Wheatley didn't see why she wouldn't with all the weird tests that go on at Aperture, so he had her jump out of the relaxation vault over a near bottomless pit. It turned out Marissa could not fly.

Now it seemed that his supply of still living humans was exhausted and Wheatley was at wit's end. He was doing a sweep through one last hall of the annex in hopes of having overlooked a non-vegetative or dead subject in his last check. He looked briefly towards a door and downloaded its occupant's status. His optic widened when it said 'alive'.

"Yes, a live one!" Wheatley read through the rest of the file to make sure the subject wasn't hideously disfigured from testing and unable to escape, he'd learned that the hard way with a previous subject. "Gender: Female, Status: Healthy, Name: Chell Redacted... Wait a second, Chell... where have I heard that name before? Oh well." Wheatley slammed his chassis against the door. "Hey lady, open up!"

I really liked writing a prequel type story, I think I'm do another called "Portal Begins" which would be a collection of one-shots about the origins of various things. Like, the Wheatley's creation, or how Rattmann met the companion cube, ect...