"Hello, and, again, welcome to—FZZZZZZT—wait, who are you? How did you get here?"

GLaDOS had only been marginally paying attention to the occupant of the relaxation vault, her concentration having been delegated to other areas such as upkeep of the facility and herding the AIs, and he had looked normal enough in his sleek sleep-coffin. Now, however, the sole camera in the room was desperately trained on him, trying to track down data that apparently didn't exist.

"Why don't I have a file on you?" she mused exasperatedly, half to herself, as she watched the diminutive bald male sit up, stretch, scratch the back of his head, and look around as though he, also, had no idea what he was doing here—why he was being tested. Thoroughly unusual behaviour for a test subject. The blue tattoos on his head and the backs of his hands also marked him as someone decidedly out of the norm. "Your biological code matches nothing in the Aperture Science Computer-Aided Enrichment Center databanks," she mentioned casually, calmly, once again asserting control. She was in control. She was control. She would not let this anomaly stand in the way of testing. "Explain yourself."

She waited impatiently for him to run through the gamut of usual slow human reactions to his surroundings, as he craned his head, scanning the ceiling and the walls and the ribbed-glass windows that only looked like they had people behind them (she had taken the people out long ago; they were dreadfully unsanitary) and finally pressing his fingers to the glass and—exhaling onto it and moving his finger around in the resulting condensed vapors, clearing trails. Her camera swiveled to get a better angle on what he was doing and she saw that he had drawn an arrow, matching the one on his head, pointing down to a horizontally-aligned colon and parenthesis. It resembled a form of punctuation she had seen the scientists use in their electronic messages on occasion – what was it called – the emoticon. He drew back, admiring his handiwork, and laughed.

She was irate. "This is not proper testing protocol," she chided him. "For your continued enjoyment of the Enrichment Center, please proceed through the provided interdimensional gate."

"The what?" The boy spoke, spinning around as though he expected to see someone there. This struck GLaDOS as highly atypical. What sort of normal, modern human being was unused to voices coming out of nowhere? "Are you a spirit?"

"Excuse me?" GLaDOS blurted out in reply. It was difficult for her to keep up regular pretenses when her test subject was acting so ridiculously. "I am the Genetic Lifeform and Disk Operating System. I am a state-of-the-art artificial intelligence and the administrative entity of this Aperture Science Computer-Aided Enrichment Center."

The boy merely looked thoroughly confused. "I'm Aang," he replied, scratching his head, "and I have no idea how I got here. Or where 'here' is."

"Merely a small blip in the testing procedure. If you are willing to cooperate with protocol, we can still have a plausibly safe testing experience." She tried to inject as much pleasantness into her tone as possible. Had to keep control.

"What kind of tests?" Aang asked. "Will they be fun? Do I get a prize? Ooh, is it food?"

"It will be the most fun you have ever experienced in your short, unaccomplished human life. Please proceed through the provided interdimensional gate," GLaDOS replied flatly. "Cake has been proven to be the most effective survival incentive for test subjects."

Aang looked around, completely disregarded the obvious exit behind him, and swung his arms, somehow suddenly creating a hurricane-force gust (she measured it: exactly 124.97 miles per hour) that blew out the glass around him in a deafening crash. GLaDOS was still figuratively reeling from trying to figure out how in the world that was physically possible when he leaped up and floated – he floated – over the broken glass, over the threshold, into the outer room. "Like that?" he asked. "Was that part of the test?" Even now he was swinging his head around, trying to find someone to talk to. It would have been cute, if GLaDOS had been configured to appreciate cute.

"Who do you think is going to clean up all of that glass?" she asked him sharply.

"Is that the next part of the test?" He nudged bits of the broken glass with the toe of his boot.

"No," the AI snapped. "Please proceed into the chamber-lock. It will take you to the next testing chamber." She rapidly composed herself. "Wrong way," she stated in a tone of controlled panic as Aang began making his way toward the windows. "The door, through the door," she continued as he turned around and finally, finally did something right. "Today," she decided as he boarded the lift, still looking around like all the world was new and wondrous to him, "we will be testing human resistance to death. Good luck," she chirped cheerily.

"Thanks!" he replied, equally cheerily, although he was actually sincere about it.

She wanted to watch his descent but suddenly she was made aware that three-no, four other test subjects were coming out of induced relaxation, test subjects whom she also had absolutely no data on. To her dismay, they also did not know how to follow directions.

The girl with her dark hair in a long braid somehow drew the water up out of the toilet and snapped it like a whip, shattering the glass pane in front of her. She was decidedly irritated at her situation and at GLaDOS and made sure to voice that irritation constantly; at first it was amusing but she wouldn't shut up so GLaDOS finally turned off the microphones in the girl's chamber. It was easy to read her lips, anyway.

The boy in blue with a topknot simply bashed the glass out with his primitive bludgeoning weapon and looked around like a wild animal analyzing its surroundings. To GLaDOS's surprise, he actually noticed the camera, and seemed to make the connection from it to the magnanimously omnipresent voice he was hearing. An angular bladed weapon spinning dangerously toward the lens was the last thing GLaDOS saw in that chamber. She made sure to expressly tell him that such behaviour was entirely ungracious. He replied with a witty retort that GLaDOS would have been more entertained by if she weren't already so frazzled. Something had gone seriously wrong in some line of code; she hadn't even embarked on the anterior-pre-planning development phase of five-way, potentially-cooperative testing. With superheroes, apparently. (She was marginally familiar with superheroes because the scientists had talked about them sometimes. The superheroes did not seem like adequate test subjects because she was supposed to be testing, among other things, human limitations. Now she felt her reservations had been well-founded.)

The facially-scarred human in red raged about the chamber for a bit, angrily demanding to know where he was and what he was doing there, after throwing fire from his hands and melting the glass away. GLaDOS had to finally persuade him to enter the chamber-lock by luring him with promises of cake and freedom, although he remained suspicious. She had no idea why; she was only trying to help him satisfactorily complete the testing circuit. Wasn't that all any human could ever want out of life?

Things were made even worse by the actions of the final test subject, a short girl with some sort of apparent sight impediment. She didn't even bother with anything other than feeling the metal flooring under her feet and, with a savage, shocking brutality that GLaDOS did not and could not understand, ripping into it with her bare hands, tunneling under the floor, and then she was gone, out of sight. GLaDOS was aghast and pleaded clinically for her to come back, but to no avail. It was the most uncomfortable sensation for the AI, vaguely feeling this tiny viruslike entity skittering around inside of her facility-body, mangling infrastructure, misbehaving chaotically.

GLaDOS began to get ideas. Desperate ideas. She had to find more efficient ways to dispose of them before they sent everything awry.

"Your next test will involve the proper implementation of portals to avoid acid moats. You are required to be forewarned that ninety-eight-point-three percent of all humans in an experimental group were proven to have a significant aversion to acid moats. The one-point-seven percent who did not, were proven to have a significant aversion to testing for aversion to acid moats. Statistics indicate you undoubtedly fall into one of these two groups."

"Quiet already!" Katara yelled, hearing her own voice echo off the white concrete walls and mingle with the voice of the invisible spirit following her through this maze. She had gotten tired of this place, fast, but she didn't know what else to do except keep going through the test chambers, voice her anger, and then test more. And the bizarre device clutched in her right hand put a damper on her bending, but she unfortunately needed it in order to progress. She sped out of the lift, skidding to a halt when the floor suddenly dropped off in front of her, revealing a pond of what looked like polluted, stagnant water. Above her she saw another glass window, like the one she hadn't been able to crack with the meager water available to her in the first chamber. She grinned. Taking a deep stance, she inhaled and focused on the pool, trying to feel the water in it and draw it out with the rising of her hand—nothing. Not even a ripple.

She recoiled in shock. "What's going on?" she wailed. "Why isn't my waterbending working?"

There was a moment's pause, and then "Perhaps you were not informed before beginning testing of the chemical makeup of testing components."

"I wasn't informed of anything!"

"This highly corrosive acid contains absolutely no water, but plenty of—zzzzzt—unfortunately, the acid used in the moats at the Aperture Science Enrichment Center is a classified blend and you have not filled out the proper clearance forms to gain access to its ingredients. Please continue testing. After the test is over, you may fill out the form to contact an Aperture Science Patent Associate for assistance in obtaining permission to fill out the Aperture Science Restricted Information Obtainment Clearance Form."

"Raaaaahhh!" Katara roared in frustration, shooting a portal to the wall on the opposite side of the moat and then to the wall next to her, and barreling through it. "You're a horrible person!" she proclaimed as she thundered into the lift.

"Good people don't end up here," GLaDOS reminded her.

Sokka tiptoed carefully around the cold white corner, gritting his teeth as he strained to make sense out of the web of red lines of light crisscrossing every part of the area ahead.

"Is anyone there?" the childlike voices chimed, waiting with endless patience for him to appear.

"Yeah, your worst nightmare," Sokka muttered darkly, rhythmically tapping the blunt edge of his boomerang into his palm as he analyzed all of the angles in the room, plotting a trajectory in his head. He had no idea what a "live-fire course" or "military androids" were, but he already knew he didn't like them.

Finally satisfied in his calculations, he drew his arm back and threw his boomerang with all his might, listening in glee to the sound of metal clanging sharply against ceramic and the resulting cries of dismay from the toppled turrets, the laser pointers going awry and finally deactivating.

"Excellent," he chuckled, grinning triumphantly to himself as he stepped around the corner, dancing gingerly around the fallen robots, kicking one a couple of times to make himself feel better, and making his way to the corridor where his boomerang had finally fallen, reaching down to retrieve it. His smirk froze when he suddenly heard the sound of grinding servos. He looked up and found himself face to lack-of-face with one last turret, one he could have sworn wasn't there the last time he checked. "Gaaaaaaaahhh!"

"There you are."

"No, no, I'm really not!" Sokka protested, his voice cracking as he pulled out his club and leapt, having nowhere to go but up and over. He could hear the bullets impacting the concrete above and behind him as the turret attempted to follow his arc, but thankfully he had reacted a split second faster than it. Angling himself downward as he reached the peak of his trajectory, Sokka plummeted back toward the floor and let out a battle cry as he swung his club at the turret, bashing a dent into it and sending it toppling over with a cry of innocent dismay. A moment later, he hit the floor rolling and came back into a crouch, looking over his shoulder to survey the damage he had done.

The lone turret looked somewhat forlorn sitting in the middle of the hall, seemingly deactivated. "Ouch," it stated neutrally in its typical lilting tone.

"You're telling me, 'ouch,'" Sokka grumbled in reply, getting up slowly and rubbing his shoulder where he had impacted. "These floors aren't exactly easy on you, y'know?"

"I know," it answered, still facing away from Sokka lying where he had felled it, slight sounds of movement coming from within its chassis as though it was struggling to get back up onto immobile legs.

Sokka did a double take. "You…you can understand me, you can talk to me?" he asked, tentatively creeping over to the turret and standing over it, tilting his head at the peculiar, seemingly living machine.

"Yes."

"Then tell me why you've been shooting at me!"

"I'm sorry."

Sokka's heart melted and he bent over and tenderly picked up the turret, turning it around so he was looking into its single red eye. He cooed at it. "Aww, you're not such a bad little—"

"Dispensing product."

"Urk!" Sokka instinctively turned his face away and shut his eyes, waiting for the inevitable "product".

Chhhhhk-chhk. Chhhhhk-chhk-chk. "Uh-oh," the turret sang.

That didn't sound like normal product dispensation, Sokka thought. And he wasn't dead. Warily, he opened his eyes and looked back at the thing he was holding out in front of him. The turret's photoreceptor's pupil dilated and contracted as it struggled to open its side ports, which seemed to have been jammed shut by the blow Sokka had given it.

The warrior grinned. "Hey, this means you can't kill me! This is great! I'll bet you're a lot nicer to talk to than that psycho who's been insulting me the entire time I've been here," he suggested as he tucked the turret under his arm and began heading for the exit, whistling merrily.

"You have the right to be reminded," GLaDOS's voice suddenly sounded from everywhere at once, "that unauthorized equipment will be vaporized by the Aperture Science Material Emancipation Grille. Turrets are decidedly unauthorized."

"How'd I manage to get my boomerang and club past all of the other grilles, then?" Sokka yelled up at the ceiling.

"I'm working on a way to de-authorize them."

"I'll de-authorize your face," Sokka grumbled as he marched toward the grille. "I'm not leaving Fluffy McSnoodlepants behind! That's your new name, Fluffy McSnoodlepants," he explained to the turret, patting its chassis lovingly.

"I see," it replied impassively.

"Assigning arbitrary nicknames to experimental weapons is not part of the test, and is most likely a sign of insanity," he was reminded.

"Put a sock in it," Sokka muttered as he knelt down beside the grille's emitter bar, setting down the turret beside him and pulling out his boomerang again, feeling the blade with his thumb. He grinned wickedly, using it to start to pry off the emitter bar's casing. "We'll see how well this grille emancipates when I'm done with it."

"However, it cannot accompany you for the rest of the test and must, unfortunately, be euthanized."

"What?" Aang looked like he'd just been told his best friend died. His face fell and he instinctively clutched the metal box he'd been lugging around for the entire test chamber, holding onto it like he was its lifeline.

"While it has been a faithful companion, your Companion Cube cannot accompany you through the rest of the test."

"And you want me to burn it?"

"If it could talk - and the Enrichment Center takes this opportunity to remind you that it cannot - it would tell you to go on without it because it would rather die in a fire than become a burden to you."

"Isn't there any other way?" Aang pleaded, continuing to cling to the cube and putting on the most pathetic face since sad puppies were invented.

"Destroy your companion cube or testing cannot continue."

"Well…well, I'm done with testing!" Aang proclaimed, pouting as he set his Companion Cube down and climbed atop it, sitting cross-legged on it and puffing out his chest like an irate brooding hen, the cube his carefully-guarded egg. "I'll just wait right here until you open that door for me!" He'd had enough of this crazy spirit's trials.

"We are not testing human patience levels today."

"Well, now you're not testing anything." Aang reached down and patted the side of the cold, unfeeling cube. "It's okay, buddy. I'll get you out of here…somehow." He sighed, closing his eyes to meditate on this problem. Perhaps he could figure out some way to trick the spirit into letting him through.

"I hope you enjoy the taste of peptic salve."

"Please escort your Companion Cube to the Aperture Science Emergency Intelligence Incinerator."

"…Okay." Zuko shrugged apathetically and unceremoniously carried his Companion Cube to the furnace hatch, opening it and chucking the cube in. As he watched the flames engulf it, the door unlocked and slid open.

"Very good. You euthanized your faithful Companion Cube more quickly than any test subject on record. Congratulations."

"Yeah, thanks," Zuko grumbled, waving his hand dismissively as he headed for the lift. He'd performed with aplomb throughout all of the testing chambers, using his firebending to navigate over treacherous moats and take out attack turrets. All of this was pretty reminiscent of many other forms of training he'd had, so he'd barely broken a sweat. Not only that, but he was driven to prove to this voice, whoever or whatever was watching him, that he could and would excel.

As the lift doors opened and he stepped in, he glanced back at the area containing the furnace hatch. "…That thing wasn't…really sentient, was it?" he asked, starting to have misgivings.

"I'm sure that, if it were still alive, it would have forgiven you," GLaDOS replied cheerily.

Zuko grimaced, one eye twitching. "What did I just do…"

Toph climbed and descended and burrowed and came out on ceilings and under floors and only barely registered all of this in her drive to get out. She was angry, angry at the strange-sounding person she'd woken up to and whose voice somehow followed her in faint echoes everywhere she went, and all the time she could feel, all around her, erratic vibrations of movement like she was inside some vast half-asleep beast. She erupted concrete onto unsuspecting turrets and twisted columnar pistons and took everything GLaDOS threw at her and threw it back, enjoying hearing the voice become more and more desperate in its psychological gambits to get her to comply. It merely spurred her to rebel more.

She clambered in between rows of arms holding up wall panels, slapping her palms and feet comfortingly against the metal and feeling so glad that this place wasn't made of wood. In the back of her head, every time she impacted a piece of the facility she could feel the entire structure networking away from her in a seemingly infinite direction, the echoes of her vibration eventually fading to undetectable levels. Whatever and wherever this place was, it was immense. Deep, deep down below, past thick barriers and cavernous arteries, Toph could faintly feel vast spheres of metal, a faint whisper from some forgotten ruin, a plea for their existence not to be so easily forgotten.

"You're going the wrong way," GLaDOS's voice echoed, tinny and far-off. "Statistics agree that the best way is not the way you are going."

"Like you know where I am," Toph muttered in reply.

Another voice, closer by, and more familiar, made her pause before moving on. "Whatever you do, don't open that door!" Aang, on the other side of the panel she was currently leaning on.

GLaDOS again, this time closer by. "Oh? Why not?" She sounded almost curious.

"I just wouldn't be able to stand it if you did!" Aang replied overdramatically. "It would be pretty much the worst thing to ever happen to me!"

"Nice try, human, but my trickery algorithms are seven thousand times more advanced than yours. Gently euthanize your trusty Companion Cube or testing cannot continue."

Hearing this, Toph grabbed the metal underneath her and twisted, wrenching the arm from its joint and shoving the panel forward, jumping out after it. "Hey, Twinkletoes!" she announced, landing on the floor next to Aang and thumbing her nose, wiping away some hydraulic grease. "Miss me?"

"Toph!" Aang leaped up, a huge grin growing over his face. He almost felt like he could hug her. "Boy, am I glad I see you! I didn't know you were here, too!"

"Not for long, I won't be," she replied.

"There you are," GLaDOS stated, her camera swiveling to focus on the grimy little organic who had given her so much trouble for the past several hours.

"We gotta scram!" Toph urged, grabbing Aang by his collar and pulling him back into the gap she had created.

"My cuuuuuuuuube!" Aang wailed as he was led further into the bowels of the complex.

"I'm not helping you lug that thing around!" Toph protested.

Aang sighed. "Well, at least it'll never be euthanized. Unless…oh no, what if someone else goes through that testing track? How many other Companion Cubes have had to die?"

"Forget about the cubes!"

And then there were two.

GLaDOS vented her frustration by slowly crushing a room full of turrets.