Aperture Laboratories ran perfectly for miles and miles around its Genetic Lifeform and Disk Operating System. Cubes, turrets and test components rolled smoothly off conveyer belts, a hundred incarnations of ATLAS and P-body were storming through their test chambers, the moron was still safely in orbit of the moon and best of all, there had been no sign of her since she had left. The labs hadn't run this smoothly since even before GLaDOS had made the life-changing mistake of initiating Chell's testing.

She should have known it was too good to last...

The first sign that something was amiss, was an alert from the turret assembly line. Ordinarily, when a turret was flawed, it was incinerated without a second thought, but from time to time, a flawed turret was extraordinary enough to warrant GLaDOS' attention, before it was destroyed.

A small camera drone hummed on a rail to GLaDOS and began filming her primary chassis, so the flawed turret could see her menacing glare. As little as she liked to admit it, it was Wheatley who taught her how effective that could be. At the assembly line, the defective turret was being held from the ceiling before GLaDOS' monitor, and the line had resumed operations behind it.

GLaDOS stared at the turret, formulating dozens of possible explanations for what had happened to it. The first imperfection was immediately apparent, even before it was deployed. The turret had two small eyes, one above and below the primary one, It was far too deliberate to be a glitch. At GLaDOS' command, the robotic limb holding the turret pressed a button, activating it, and dropped it to the floor. Four triple-jointed legs with flat, circular feet deployed, and the turret landed confidently, without so much as a wobble.

"Depth perception? Gyroscopic stabilization? GLaDOS commented, "You're nothing but a killing machine. Turrets aren't supposed to kill people, they're supposed to fire at them blindly, terrifying and seriously wounding them, otherwise it's not really science." The turret had begun skittering around, spider-like, before the monitor. More than once, GLaDOS tilted up a floor panel to prevent it from escaping. "I already have plenty of killing machines, so I've no need for you, but thanks for stopping by..." GLaDOS concluded, with something of a threat in her voice. Sure enough, a moment later, the metallic limb on the ceiling reached down for the turret again, and the incinerator on the other side of the room opened hungrily.

The turret jumped around to face the limb and squeaked in panic. It deployed its firearms. Unlike its siblings, the segments on each side of the defective turret span 90 degrees, revealing a pair of high power rifles on each side. The turret span around in a circle just once, firing five bullets as it did. To GLaDOS' astonishment, each bullet destroyed one of the room's security cameras, two of which even ricocheting off the walls to bypass the observation room.

GLaDOS stared at the static on her screen in shock. Someone could only have designed something so efficient, but why? She quickly raced through her extensive list of enemies. That hussy who had tried to steal her old job by flirting with Cave Johnson was dead, all the Black Mesa representatives she had met with were dead, the scientists who put her mind into a computer were dead, as were the ones who fitted her with inhibitor cores, and the humans ATLAS and P-body had helped her recover for testing were all dead. GLaDOS took a moment to pride herself on how few people survived being enemies with her. All that left was Wheatley, whose greatest creations could barely sit on buttons, and Chell.

Of course. GLaDOS should have known better than to let that monster walk free, she must have come back to finish what she had started and kill her a third time. GLaDOS quickly had ATLAS and P-body assembled at the production line.

"Ok marshmallows, find that turret and smash it a lot!"

ATLAS stood to attention and gave a rigid salute, even though GLaDOS couldn't see him. His sudden stop caused P-Body to walk right into him, causing both robots to collapse in a metallic heap. If GLaDOS had lungs, she would have sighed at the robotic babbling she heard over her coms system. She pulled up the assembly line's output history, to find out what she was dealing with.

Sure enough, an entire set of detailed blueprints had been hidden in the assembly line's software. Before thoroughly erasing it to prevent any more rogues, GLaDOS extracted her own copy to study. The design didn't teach her much she hadn't already seen. The turret's second and third eye gave it absolute firing precision, something its cyclops siblings were deliberately lacking. It had four, fully flexible legs with magnetic feet, meaning it could go virtually anywhere, and its stabilization made it far more sure-footed than a standard turret. This thing was shaping up to be a real pest.

All turrets were made to be self-aware, although this one was able to act on its impulses, rather than involuntarily shooting at anything that moved. The final quirk the turret possessed were a series of data files stored in its memory. They included several maps of the more modern laboratories, factoring in their ability to reconfigure at GLaDOS' will, several extensive schematics of GLaDOS' chassis, and some of Chell's testing logs, from before she had murdered GLaDOS the first time.

The final file was a video. Opening it, GLaDOS was greeted by a man with a memorable mop of wild, black hair and a mad look in his eyes. The light on GLaDOS' chassis flared, as though she were rolling her eyes. "Oh no... not this idiot again..." She moaned.

"Hi..." Doug Rattmann nervously began, as GLaDOS started the video. "If this file is being watched... then... then things haven't gone well. I just saw GLaDOS get destroyed, and Chell put in stasis... But GLaDOS' servers are still intact, I don't think anyone actually knows where they are, probably not even her."

GLaDOS squinted angrily. "Well maybe I don't care where they are..." She muttered to herself.

"But that means that one day, she might come back online..." Rattmann continued. "And if that happens, we'll need Chell, and if Chell fails... well... well then we'll need you. Your name is Luke. That's... that's kind of a joke, it was her idea." Rattmann leaned to one side, revealing a Weighted Companion Cube resting on a surface behind him. "I've given you the tools you need to stay one step ahead of GLaDOS, and the tactical skills to fight back, when you can. I hope she never wakes up, and that if she does, I hope Chell can handle her, but if not... well good luck."