A/N: Well I'm back. I hope everyone had a nice Christmas and new year. I planned to post sooner, but the festive period is insane when you work in pharmacy.

Let's crack on! Recognisable dialogue in this chapter comes from Portal and Lab Rat.

2010.
The Ultimate Systems Crash.

After Chell's departure into the broken transport tube, Doug had backtracked to Test Subject Observation and Care, breaking the window through to the conference room with its looping slide show. He let himself out into the corridors beyond, wary of cameras. He hadn't passed that way since GLaDOS had taken over.

"How long has it been since I took my meds?" he asked softly.

"About fifteen minutes," the cube replied, sounding sullen.

"Hmm. It'll be a while before they kick in then. I think they've technically expired."

"I'm worried. What if them being past the expiry date means they have unknown side effects?"

Doug shook his head, as if trying to jar the notion loose. "It's worth the risk," he declared firmly, believing it despite the cube's doubts.

Slipping through another door back into the maintenance areas, he broke into a run. He had a place in mind where he could catch up with the girl, but he had to beat her there. After a moment, he found a door that he'd marked with an X, and typed in his code. The door opened out into a shabby area drenched in red light: one of his old sleeping dens. His makeshift cardboard bed was still there, looking as uncomfortable as it had felt.

Unsure how far behind she was, he hurriedly took a plastic water bottle from the bag the cube sat in, tipping what was left in it into one of the large containers he'd kept in the den. Then, to indicate that it was for her benefit, he scribbled another HELP on the wall next to the older graffiti.

Throwing the empty bottle back in the bag, he continued on down the short corridor to a large gap in the wall. It overlooked a series of huge, slow-moving pistons, rising and falling with loud, dull clangs. A broken ladder led to the way forward, up to a doorway high on the wall. Checking that the girl was not in the room, Doug turned and climbed down the shorter ladder that served as the only entrance to the den for those who did not have a portal gun. He hopped onto the piston nearest the way out, riding it up, then making a leap for the rungs of the wall ladder before he had time to over-think it. He scrambled to the top and pulled himself into the relative safety of the corridor beyond.

There was a mesh wire gate nearby leading to a darkened area beyond more of the clear transport tubes. A padlock hung open on the latch. Doug swung the gate open and closed it behind him. He couldn't lock it from that side, but most likely the girl would walk straight past it. He turned, winding his way through the tubes to the dim area beyond. Running his fingers along the wall, he managed to find the air conditioning duct he was after, and he pulled himself into it.

"Where are we going?" the cube asked.

"Away. The rest of the girl's route is pretty well mapped out from here," he replied, navigating the vents. "I was able to get into the piston rooms and backtrack to areas I couldn't reach initially. She has a small turret trap ahead of her, but it's pretty straightforward. I'm sure she can get through it."

"Then what?"

"She'll reach another suite of offices where she'll need to bypass a rocket launcher, but the walls are glass there, so her way out will be simple. After that, she'll be in the tunnels that used to lead to the breaker room."

"You mean, the ones She flooded with toxic waste?"

Doug nodded, peering through a grid in the floor to check his location. "That's where we're going. We have to wait for the girl to catch up."

"Do you really think she can?" the cube asked.

He nodded again, more firmly. "I have faith in her."

They kept going in silence, Doug pulling the cube behind him while he crawled through the vents. Once they were out, he swung the bag on his back again, breaking into a jog as he wound his way along the corridors and walkways. Eventually, he stopped at another keypad door, typing his code in. The door opened out on a wide platform in an industrial-looking area. Once, it had been a maintenance access point, high above the pathways below. Now it was simply a platform above a river of sludge.

"She should approach from there," he said, pointing at the narrow route on the opposite wall.

"When?" the cube wanted to know.

"Soon. She will have gotten past the turrets by now." He turned away, looking up at the tiny grate that would serve as her exit point via portals. "After that, she's on her own. There's no way up from here except through that, and we won't fit."

"The main chamber is more closely guarded than it used to be," the cube spoke up. "Like the pharmacy wing."

Doug nodded in grim agreement. "That's my fault. I tried to get into the breaker room a few days after GLaDOS was activated. Then when it occurred to me to try and steal more medication, I found she'd learned enough from that experience to block all routes to the pharmacy."

"I remember."

He shot the cube a raised eyebrow. "You do? But you weren't around then."

"Not in body," it admitted, "but I'm part of you, Doug, don't forget."

He faced forward again, passing a hand over his chin. "I do forget sometimes. It's difficult not to when you…when you sound like her."

Taking a deep breath, he pulled his leaky black marker pen from his pocket and approached the wall. His hand halted a few inches from the concrete, shaking slightly as his breath caught.

Last chance, he thought. Last chance to keep her safe. She'll never have to come into contact with GLaDOS if you don't draw that arrow.

"If I don't draw it," he murmured aloud, "none of us will escape. We won't even have a chance."

He'd been trying so hard over his period of isolation, trying to forget who she was and what she meant to him. At times he'd succeeded, at others he was pretending, attempting to convince himself that he was in control. In that moment, the moment that mattered the most, he knew exactly who she was. Drawing the first line felt like the worst kind of betrayal.

He persevered until he'd gotten the most out of the steadily-dying marker pen: an arrow pointing up towards the grate, surrounded by several smaller, stylised ones. With every line he drew, an apology fell from his lips. The cube remained respectfully silent throughout.

Dropping the pen into his lab coat pocket, Doug withdrew into the corridor, pulling the door almost closed, leaving a tiny crack to see through. He wasn't sure how long he waited. The medication had kicked in enough to stop the background hum of voices, and everything felt still, an intimidating level of silence that he'd almost forgotten after three years of noise. The cube – which had always had the strongest, most consistent voice – would be the last to fade.

Eventually, he heard the faint pop of a portal opening. Then there came the sound of the girl's footsteps, and he pulled the door closed, wincing at the beep it made as it locked. He stood motionless, ear against the cool, painted surface. There was a second portal sound, then the tap of her leg springs close by. Doug held his breath as the door handle moved, his hand hovering aimlessly next to it. Gently, he pressed his palm to the door, as if he could reach through and touch her shoulder, her hand, her hair…anything to remind himself that she was really there.

He heard her walk off, her steps pausing a short way away. Most likely she was examining the arrow. Then they came back twice as fast, and a sharp knock on the door made him jump back in alarm.

"I know you're in there!" she said fiercely, her voice raspy with disuse. "This ink is still wet, and there's nowhere else for you to go!"

Doug sank into a crouch, his heart hammering like one of the pistons back in engineering. He clasped a hand over his mouth, a deterrent against calling out to her.

"Look, just…please. Please come out. I just want to see with my own eyes that…someone's still alive." She sighed heavily, the sound muffled by the door. "I don't know where you're sending me, but…I'm beginning to think that…maybe it isn't a way out?" Her voice was tentative, unsure. "I don't know what you're up to, but…no doubt you have your reasons." There was a pause, heavy and awkward. Then she spoke again, this time in an angry, bitter tone. "You know what? Fine. Stay in there, I don't care. I'm going to find and deactivate that psycho supercomputer, then I'm getting out of here. Feel free to do the same, you cowardly asshole, and hope that I don't die trying."

He listened to her stomp furiously away. She fired two portals, and he heard her step into some kind of squelchy gunk, emitting a soft noise of disgust.

He lowered his hand, breathing so fast he thought he might be having a panic attack. His mind was whirling, trying to regain control of his careful self-delusion. But then, just when he thought he'd got it back, it all crumbled. Stumbling clumsily to his feet, he typed his code into the keypad and wrenched the door open. Through the vivid cerulean hole in the wall, he saw her picking her way through what looked like mud, raising her portal gun to aim at the wall higher up, out of the trench she was currently in.

"Wait!" he cried, rushing forwards. But he'd timed it badly, his word getting lost in the gentle noise from the portal device as she fired. The portal disappeared, and he found himself facing concrete again.

"Don't do it," the cube warned.

For perhaps the first time, Doug ignored it, lunging to stand under the tiny grate. "Chell!"

But she had gone. Shortly, there came the sound of turret voices and gunfire, and he sank to his knees, hands shaking.

"What have I done?" he whispered.

"What you had to do to survive," the cube told him sagely, calm despite the tears that were now pricking his eyes.

Feeling his guilt as a tangible weight on his shoulders, he closed his eyes, drawing in a ragged breath as he listened to the turrets spraying bullets above.

"I'm not so sure it was worth it. Not if I have to go on like this."

"There's still hope."

Doug shook his head. "Not if she's…" He couldn't say the word.

"Do you trust her?"

"Yes."

"Really?"

"Yes!" he declared vehemently. "I just…I'm afraid. Of…of losing her. It would be all my fault. I would have killed my best friend, the only person who has ever looked out for me in this place."

In the room above, the turrets had fallen silent. Doug looked up, biting his lip as he waited for the one sound he needed to hear. The moment stretched agonisingly on, but then there it was: the dull pop of portals opening, followed by the faint sound of clothing rippling in the breeze.

"She must be using momentum techniques," he muttered aloud.

"See?" said the cube. "She's fine. But what about you?"

That was a good question. What about him? He already had the answer to that: he was a mess.

"I…" he began, considering. "I think…I need to paint something." He scrambled to his feet, heading back through the door. "All we can do now is wait."

He broke into a run, navigating the corridors with ease, the layout of the place fresh in his mind.

"Stay to the right!" the cube piped up as they approached a fork in the path. "Turrets ahead on your left."

Doug veered right, seeing the scarlet laser sights ahead. "Whatever you say."

Before long, he had reached his room of murals, its sole blank wall staring invitingly at him. His pots of paint, taken long ago from a decorator's closet, waited patiently for him, along with a selection of brushes and his now-battered Art Therapy book. He set the cube down on top of a filing cabinet he'd dragged there, dropping his bag by the side.

Doug stared at the wall, the canvas that had remained blank for so long because he hadn't known what to put on it. Suddenly, he knew exactly what should go there. He could already see it, he just had to make it a reality.

This won't take long at all, he thought to himself. Just as well.

Opening the paint pots, he got to work, both on the painting and on focusing his mind.

Chell had had enough of being manipulated, either by GLaDOS or the mysterious message-writer.

The last straw had been the arrow out of the sewer-like area, its still-wet ink and the nearby locked door throwing her into a whirling tornado of emotions: first desperation, then acceptance, then a sudden sharp flare of anger.

After she had dealt with the turrets in the room above, she regretted what she'd yelled. Chances were the person had already run out of earshot, leaving her ranting at an empty corridor. But if they had been there, she wasn't surprised that they hadn't made themselves known after she'd called them a cowardly asshole. She hadn't meant it, not really. She was just fed up, and she'd begun to suspect where the seemingly-helpful graffiti was leading her. At first, she'd been angry, scared that it was a trap, but now there was nothing she wanted more than to find GLaDOS and shut her down. Chell had well and truly reached the end of her tether.

She crossed the walkway over the turret room with slow, cautious steps. The room seemed to stretch endlessly upward, fading into misty blue depths that were broken up only by dozens of other walkways and vine-like, draping cables. A door awaited her at the end. Just a simple, unlocked, push-the-handle door.

She raised an eyebrow as she approached it. She wasn't sure exactly what she'd been expecting, but it seemed rather anti-climactic after everything she'd been through. Granted, it was flanked by warning signs, but there were hundreds of those about.

Shrugging, Chell opened it, stepping into a bleak, grey-tinted corridor. It wasn't entirely unlike the corridors on the management level where she'd worked, just colder and more clinical somehow. Doug had once described it as dull and depressing, and now she saw why. No wonder he'd hated working there.

She turned a corner, discovering an alcove with three chairs in it, facing large windows through to the main chamber. Sidetracked, Chell approached them, her mouth falling open as she saw GLaDOS's fortress for the first time. It was a cylindrical monstrosity, rising up from the floor on struts, reachable only by the glass-walled corridor nearby. More walkways surrounded it, criss-crossing upwards into the absurdly-high ceiling. The Aperture Laboratories logo was proudly stamped vertically on the side.

Wetting her dry lips, feeling her heartbeat speed up in part anticipation, part fear, Chell backed out of the alcove, climbing the three or four steps up to the corridor beside it.

'Caution: Wear your respirator,' a sign by the door helpfully advised.

Chell scoffed humourlessly. That had gone down well.

Her steps down the glass corridor were slower still. The door at the far end was open, and she could see the A.I. hanging from the ceiling, swaying gently. She was surrounded by cables, and Chell could see several cores attached to her, similar in design to Wheatley. As she got closer, she noticed that the room was full of huge, widescreen monitors flashing up a variety of images too fast to comprehend.

Unable to put it off anymore, she stepped through the particle field across the door. There were desks just inside, the computer keyboards and stationary abandoned just like everywhere else. On the left-hand side there was a bright red telephone. Chell stared at it, a long-ago memory surfacing. Her third week working at Aperture, the internal phone lines going down, Doug's future colleague, Henry, yelling at Marlene…

"You don't understand… If the phones are out then that means the red phone is out too!...You don't even know what I'm talking about…"

She blinked. Clearly, the phone had been intended to be an emergency helpline, one that the scientists had relied on. In light of what had happened to them all, it seemed a ridiculously inadequate failsafe.

"Well, you found me," GLaDOS said, pulling her out of her memories. "Congratulations. Was it worth it? Because despite your violent behaviour, the only thing you've managed to break so far is my heart."

Chell narrowed her eyes, carefully walking a little closer. There was a kind of observation deck in the middle of the room, and a strange little room on struts off to one side. At the far end, she spotted an incinerator like the one she'd dropped the companion cube into.

GLaDOS turned to her, fixing her with a stare from her bright yellow optic. "Maybe you could settle for that and we'll just call it a day," she went on. "I guess we both know that isn't going to happen. You chose this path. Now I have a surprise for you."

She backed up a little, wary of what the A.I. might be planning. Chell's anger had made her determined to come and confront GLaDOS, but now that she was actually doing it, she wondered if she'd been a little hasty. She had no defence against neurotoxin, and no knowledge of how to deactivate a homicidal computer.

'Deactivate' is a loose term, Chell, she reminded herself firmly. Rip her wires out if you have to.

Still, she wished she had something more heavy-duty than a portal device.

"Deploying surprise in five, four..."

One of the cores fell off with a dull clunk, sparking as it hit the floor. The sight seemed to halt both of them in their tracks.

"Time out for a second," GLaDOS said. "That wasn't supposed to happen."

Chell raised a sceptical eyebrow. She had heeded Doug's advice not to talk to GLaDOS, and she wasn't about to start now, however conversational the A.I. was suddenly being.

GLaDOS rattled on, unperturbed. "Do you see that thing that fell out of me? What is that? It's not the surprise. I've never seen it before. Never mind. It's a mystery I'll solve later...by myself...because you'll be dead."

Wait, Chell thought rapidly. That thing is part of her…

She darted forward, picking the sphere up with the gun's magnetic field. It stared at her with a luminous purple optic. Unlike Wheatley, it didn't speak.

"Where are you taking that thing?" GLaDOS demanded.

Chell ignored her, running for the incinerator.

"I wouldn't bother with that thing," GLaDOS advised matter-of-factly. "My guess is that touching it will just make your life even worse somehow."

The incinerator had a protective cover that seemed impossible to move. There wasn't a control panel in sight. Keeping panic at bay, Chell glanced around the rest of the room. On a whim, she hurried for the steps up to the strange room on struts, leaving the core on the floor. To her immense relief, there was a button there that opened the cover, but only for a short time. No doubt it was an attempt at a safety measure for the workers. To Chell it was an inconvenience.

She ducked back out of the room to fire a portal over near the incinerator, opening the second one on the wall beside her.

"I don't want to tell you your business," GLaDOS put in, implying the exact opposite, "but if it were me, I'd leave that thing alone. Do you think I am trying to trick you with reverse psychology? I mean, seriously now."

Chell activated the button, jumped through the portal and picked up the core, sending it plummeting down into the fire. She heard it explode, then the room gave a mild shudder. Startled, she whipped round to see if her actions had had any effect.

"You are kiddingme," the A.I. exclaimed, her voice glitching on the first word. "Did you just stuff that Aperture Science Thing We-Don't-Know-What-It-Does into an Aperture Science Emergency Intelligence Incinerator? That has got to be the dumbest thing that…whoa. Whoa, whoa, whoa." Her voice distorted again, reducing to static.

Then GLaDOS chuckled, a sly, low, triumphant sound. "Good news," she said, her voice suddenly less like a computer and more like the human woman who served as her foundation. "I figured out what that thing you just incinerated did."

Chell could barely remember Caroline, but there was no mistaking that the voice was very familiar.

"It was a morality core they installed after I flooded the Enrichment Centre with a deadly neurotoxin to make me stop flooding the Enrichment Centre with a deadly neurotoxin."

At her words, Chell felt as if someone had poured ice water down her spine.

The morality core…I destroyed the morality core, she thought, starting to panic. The only semblance of a conscience she has. I'm dead. Why the HELL didn't Doug tell me what it looked like?!

Deep inside though, she knew it wasn't Doug's fault. She'd known about the morality core, she should have considered that the sphere she'd burned might have been it.

"So," the A.I. went on, "get comfortable while I warm up the neurotoxin emitters."

Vents around the room began spitting out clouds of noxious, green-tinted gas and a timer appeared on the monitors. Unable to simply stand and do nothing, Chell broke into a run, circling the room while she tried to think of a way out.

"Huh," GLaDOS said. "That core may have had some ancillary responsibilities. I can't shut off the turret defences."

Chell skidded to a halt as a rocket launcher core rose up out of the floor in front of her. Its optic turned red as it spotted her and she dove to one side as it fired. The rocket hit the wall behind her, showering her with chips of concrete.

The A.I. seemed to be regarding her behaviour as entertainment. "Oh well," she said carelessly. "If you want my advice, you should just lie down in front of a rocket. Trust me, it'll be a lot less painful than the neurotoxin."

We'll see which one of us can handle being in front of a rocket, Chell thought determinedly.

She fired two portals in the wall, one at ground level, one opposite GLaDOS. She stood in front of the one at ground level, holding her breath as the neurotoxin hissed overhead. The rocket launcher's laser sight found her, and Chell was pleased to see that it lined up nicely with the swaying robot. She once again dived aside as it fired, rolling to her feet just in time to see the rocket strike the side of GLaDOS's chassis.

Her voice glitched again, her optic momentarily going dark. Another core fell off, bouncing up to rest on top of a couple of pipes. Chell fired a portal behind it, reaching through to pick it up. It chirped at her in a high-pitched, childlike voice, asking an endless stream of questions that she ignored. Using the same method as before, she sent it spinning away into the incinerator. There came a harsh, robotic scream that made her wince.

"You think you're doing some damage?" GLaDOS snapped harshly. "Two plus two is...ten. IN BASE FOUR! I'M FINE!"

Coughing, Chell looked up at her with wide eyes, unsure if she was winning or not. Her lungs were burning, her eyes stinging. She knew, without the helpful countdown to remind her, that she was fast running out of time.

I can't do this, she thought, trying not to lose her nerve. Panic wouldn't help her. I don't know what I'm doing.

She ran back to the wall, firing the portals to get the rocket to hit GLaDOS again. It was the only plan she had.

"I let you survive this long because I was curious about your behaviour," the A.I. told her as she went. "Well, you've managed to destroy that part of me. Unfortunately, as much as I'd love to now, I can't get the neurotoxin into your head any faster."

No need, she thought bitterly, diving aside as the rocket passed her. It's doing a good job on its own.

Another core flew off the chassis, lifted up onto a platform next to GLaDOS's spinning processors by a malfunctioning gravity field. Chell set about retrieving it, giving herself a run-up and leaping through a portal to grab it. As she sent it the same way as the others, it recited what sounded like a cake recipe.

The room shook again as the core exploded, causing her to cling on the incinerator for support. Another rocket came her way and she jumped backwards out of its path.

In the centre of the chamber, GLaDOS began to imitate a cough. "Neurotoxin..." she spluttered. "So deadly...Choking..." She gave a vicious laugh. "I'm kidding! When I said deadly neurotoxin, the 'deadly' was in massive sarcasm quotes. I could take a bath in this stuff…"

Her voice cut off, then sped up as Chell redirected another rocket her way. The test subject watched a fourth core fly up away from the chassis, stopping to hang stubbornly in mid-air, out of reach. She spat on the floor, trying to rid herself of the foul taste in her mouth, but it did no good. She had minutes left, if that. Clenching her teeth, she once again placed portals in strategic positions, emerging high in the wall to grab the core as she fell down.

"Who's gonna make the cake when I'm gone?" GLaDOS asked sharply. "You? Look, you're wasting your time. And, believe me, you don't have a whole lot left to waste."

Chell disregarded that as she jogged back to the incinerator, her vision beginning to swim, nausea seeping through her stomach.

"You've been wrong about every single thing you've ever done, including this thing," GLaDOS declared.

Maybe it was Chell's toxin-addled brain, but she thought she detected a hint of panic in the robot's tone.

"You're not smart. You're not a scientist. You're not a doctor. You're not even a full-time employee. Where did your life go so wrong?"

Chell didn't react, running up the steps to the incinerator button.

"Are you trying to escape?" GLaDOS asked with a faint chuckle. "Things have changed since the last time you left the building. What's going on out there will make you wish you were back in here. I have an infinite capacity for knowledge, and even I'm not sure what's going on outside."

Coughs racking her body, Chell ignored the A.I.'s bluff, throwing the final core, (a red-optic one that growled and snarled at her), into the fire.

The room shuddered again, and the monitors and cables fell away from the robot's chassis. She hung limply from the ceiling, sparking. She was still talking, but her voice was warped, speeding up into something unrecognisable. Blue and green arcs of lightning shot out of the processors above her, which began to spin even faster, losing parts of their casing. She was breaking apart, her voice now slowing like a broken record player.

Chell slumped to her knees, barely able to breathe. Something strange was happening above, a tornado of false gravity fields, debris and neurotoxin, which was pulling GLaDOS up higher and higher towards the ceiling. The suction plucked the portal gun from her hands, whipping her hair around her face. Realising what was about to happen, Chell looked desperately around for something to hang onto. Her fingers scraped uselessly at the floor as she too was picked up and carried upwards.

There was a deafening explosion as the ceiling blew apart, and Chell was blinded by severe, white light. She closed her eyes tight, feeling the wind whistle past as she was pulled further up. She felt herself falling in an arc, no longer supported by the malfunctioning gravity fields, and just had time to rasp out a cry before she hit the ground. The impact knocked the breath out of her, sending bruising pain shooting through her tired limbs. Her head scraped along the ground. Woozily, she opened her eyes.

Vaguely, she recognised the entrance to the parking lot, and felt the hot discomfort of the sun-warmed asphalt she was lying on. Debris rained around and on her, pieces of GLaDOS's chassis and other parts of the main chamber. Some of them were steadily burning.

I need to move, she idly thought to herself.

On muscles that were trembling relentlessly, she tried to push herself up, but her arms gave way and she slumped back down, rolling onto her back. The fresh air was helping clear the neurotoxin from her lungs, but she'd breathed enough of it to make her feel drastically sick and more than a little fragile. Her eyes fluttered closed again, and she felt unconsciousness creeping up on her.

At least I fixed your mistakes, Dad…

A/N: I can't believe we've reached the end of Portal already. Not to worry though, there's a lot more of this story to come.

Fun fact: this chapter includes the single line of dialogue that shaped Chell's role in pre-GLaDOS Aperture for this story: 'You're not even a full-time employee'. Hence why I could only give her part-time hours :)