Portal 2 storyline

Portal 2 almost directly follows the events of Portal from Chell's perspective, although being set several years (possibly decades or centuries) after the events of Portal. The rest half of the game follows Cooperative Testing Initiative, whom GLaDOS accompanies through the Cooperation Test Initiative.

Single-player campaign
The single-player campaign is set directly after Portal and Portal 2: Lab Rat, and right before the cooperative campaign.

Prologue
Fifty days after the events of Portal, Chell is reawakened by an unidentified announcer. In compliance with "state and federal regulations", Chell is instructed to perform a mandatory physical and mental wellness exercise. Chell is then instructed to return to bed.

The Courtesy Call
Set several years after Portal. The announcer wakes Chell up once more, and tells her that she has been in suspension for "9. 9. 9. 9. 9.-" only to meet Wheatley and helps him escape with her. The original Portal chambers are reintroduced, only damaged and with plant overgrowth sprawling along the walls. They are guided by the same announcer, using pre-recorded messages.

At the end, GLaDOS is accidentally reawakened and starts building new test chambers.

This chapter includes:
 * Aperture Science Extended Relaxation Center.
 * Decrepit Test Chamber 00 through Decrepit Test Chamber 08.
 * GLaDOS' Chamber and Main Breaker Room.
 * Incinerator Room.
 * Decrepit Test Chamber 19.

The Cold Boot
GLaDOS introduces new tests. They primarily include Thermal Discouragement Beams and Aerial Faith Plates. This chapter includes GLaDOS' Test Chambers 0 to 8.

The Return
Chell is put through more tests. The Hard Light Bridge and turrets are introduced.

Meanwhile, Wheatley formulates a plan to escape. GLaDOS spouts out information regarding the building, as well as attempting to trick Chell once more. GLaDOS also mentions of finding two people with Chell's last name, coincidentally a man and a woman.

This chapter includes GLaDOS' Test Chambers 9 to 17.

The Surprise
Chell is given a "surprise" as hinted by GLaDOS, which is the complete absence of one.

Meanwhile, GLaDOS once again attempts to make Chell stop by making her feel bad, especially now GLaDOS decides to include Chell's unknown parents into their conversations.

The Escape
Before GLaDOS can kill Chell, she and Wheatley escape. They eventually sabotage GLaDOS's turret and neurotoxin manufacturing facilities. Chell and Wheatley force a core transfer on GLaDOS so that Wheatley can take control of the facility so they can both escape.

However, Wheatley becomes enraged when GLaDOS tells him that he did nothing and that Chell did all the work. He then traps GLaDOS in a potato battery. Afterwards, GLaDOS explains that the scientists of Aperture science created Wheatley mainly to slow GLaDOS down before the morality core was created to stop her from killing the humans. He was made to produce bad ideas. GLaDOS takes it too far and calls him a moron, prompting him to throw GLaDOS into the lift with Chell and smash on it with his 'fist', screaming "Could a MORON PUNCH. YOU. INTO. THIS. PIT?! Huh? Could a moron do THAT?", until it breaks and goes into freefall, deep into the bowels of Aperture Laboratories.

The Fall
Chell and GLaDOS fall down into Aperture Science's old test areas, back when Aperture Laboratories was instead known as Aperture Science Innovators, and get separated from each other. She is guided by pre-recorded messages by Cave Johnson (the former CEO of Aperture Science) and occasionally, his assistant, Caroline. She activates the flow of the Repulsion Gel, and begins testing in the first Enrichment Sphere, where the Repulsion Gel, the first design of boxes, buttons and switches is shown.

The Reunion
Chell manages to find GLaDOS being eaten by a crow. With no other choice, Chell skewers GLaDOS onto her Portal Gun and continues through the Johnson-era test chambers with the AI in tow. As they go up the Enrichment Spheres, they discover that Aperture Science lost money over the years, and witness how the quality of the tests chambers falls dramatically, while they activate the flow of the last two gels.

Meanwhile, as they listen to more of Cave Johnson's recordings, GLaDOS recovers the long-suppressed part of her personality based on Johnson's faithful assistant, Caroline.

The Itch
Chell and GLaDOS return near the surface to Wheatley's redesigned Aperture Science Enrichment Center, while making the gels available in the Enrichment Center. Wheatley has taken control, but in his incompetence has failed to maintain the facility's nuclear reactors which are now in meltdown. Instead of properly maintaining the facility, Wheatley has been busy with his own creations such as the cube-turret hybrid known as "Frankenturrets" by developer commentary.

GLaDOS attempts to destroy Wheatley with a logical paradox, but fails due to Wheatley's already-poor grasp of logic. The mad AI forces Chell to go through his own ineptly designed test chambers, followed by more lethal chambers stolen from GLaDOS' collection.

The Part Where He Kills You
After several tests, Wheatley finds out about the Cooperative Testing Initiative and takes it upon himself to kill the two. Chell manages to escape thanks to her skill with the portal device and a timely splatter of Conversion Gel.

As they make their way through the maintenance areas, the two come across a cache of un-incinerated corrupt personality cores. GLaDOS makes a plan to force another core transfer in order to return back to her original body, as well as making a deal to release Chell once they do so. Upon reaching Wheatley's chamber, a battle ensues. Chell redirects bombs to Wheatley as GLaDOS delivers corrupt cores. After attaching three cores, Chell increases Wheatley's corruption to one hundred percent. A core transfer takes place but results in another stalemate. Chell reaches for the Substitute Stalemate button, but Wheatley expected this and placed bombs as booby-traps.

Chell gets thrown across the room as the reactor meltdown enters its final phase, shaking the chamber apart. A full Moon appears through a breach in the roof, allowing Chell to shoot a portal at its surface (Cave Johnson said prior that lunar dust was an excellent portal-conducting surface). The vacuum of space sucks Chell, Wheatley, and the Space Core through, as Chell hangs onto Wheatley's tethered core to survive. Unseen, GLaDOS successfully performs the core transfer and stabilizes the reactors. She knocks Wheatley out into space and drags Chell back to safety before closing the portal.

The Credits
Chell wakes up in an elevator, as GLaDOS tells her that "being Caroline" taught her a valuable lesson- that Chell was her best friend. She supposedly deletes Caroline and immediately returns to her darker state, saying that she originally considered killing Chell for what she has done to her, but instead decides to transport her outside of Aperture and demands that she "never return", for the sake of not bothering her again. There the co-op bots make an appearance with GLaDOS.

The elevator rises and Chell meets singing turrets along the way. After the elevator rises one floor up from the first set of four turrets a frankenturret can be seen on a catwalk in the background. Finally reaching the surface, Chell steps out from the elevator and into a field. Unexpectedly, the original Companion Cube, covered in soot from the incinerator, is thrown out of the outhouse after Chell.

Cooperative campaign
The co-op campaign is set after the events of Portal 2's single player campaign. In it, two testing androids of the Cooperative Testing Initiative carry out a series of tests in four different courses, each consisting of about eight or nine chambers. At the end of each course, GLaDOS sends the androids outside of the testing chambers and into the facility itself, claiming their help is needed to retrieve several Compact Discs "innocently" left lying around by the humans. In reality, she appears to be using the androids to help her gain control of the facility. After each out-of-chamber task, both androids are self-destructed and then reassembled in the Hub.

Team Building
ATLAS and P-body are put through a series of simple tests, designed to promote cooperation and teamwork through the use of Super Buttons and Thermal Discouragement Beams. The final test sends them down to the basement of the facility to activate a targeting computer, which locates a small group of objects.

Mass and Velocity
This test course focuses on advanced "flinging" techniques, teaching ATLAS and P-body to not only form complex chains using all of their portals, but also timing to allow one to catch an object mid-fling when it is dropped by their partner. The final test involves retrieving a set of blueprints, which GLaDOS states are of no concern to the androids.

Hard Light Surfaces
The next test course involves the Hard Light Bridges, teaching ATLAS and P-body to use them as both platforms and shields. The final test has them download a security code which GLaDOS attempts to drown out with a series of "blah" noises.

Excursion Funnels
The Excursion Funnel test course, as with the previous ones, teaches the cooperative use of funnels and their reversal function. The final test mixes the use of the funnels and Hard Light Bridges as shields in order to reach a power station, which is activated to provide power to the final course.

Mobility Gels
With the previous courses finished, GLaDOS can now access a vault in the lower levels which contains hundreds of human test subjects. She has determined that, given their inability to die, ATLAS and P-body just aren't the same as human test subjects. They are sent to open the vault. These final chambers take elements from all the previous test courses while adding the Aperture Science Mobility Gels as an additional element. In particular, the creative use of Hard Light Bridges and Excursion Funnels in conjunction with the gels is a necessary aspect of completing the test. Upon reaching the vault, ATLAS and P-body open it by making similar gestures to the camera installed on the lock. GLaDOS claims to have more work for them as she destroys them. As the credits roll, GLaDOS scans the identities of the test subjects and makes remarks about them, both positive and negative, though in the end the comments are apparently all directed at one subject.

Trivia

 * Chapter 9 is only given a full name when it is reached; before that it is only known as "The Part Where...".


 * During the prologue, the first time you look at the art on the wall it shows a cabin and some mountains. After waking up for the second time, if you look at the art a moon will be painted on it, effectively foreshadowing the ending sequence.


 * At the very end of Chapter 6, it is possible to completely skip over the part where the player saves GLaDOS from the bird. Using some well aimed portals, it is possible to fling yourself over to the elevator. This does not affect the story, as when the next screen appears, GLaDOS is on the prong of the portal gun.


 * A developer commentary node near the beginning of the game states that there is an impossible space in the game. This space can be found in Chapter 9, being in the form of the large, moveable room where the failed Turret ambush takes place.