Still Alive
It doesn't take an Aperture scientist to piece together that GLaDOS resumes her role as the omnipresent antagonist in Portal 2. The lark-like melody "Still Alive" at the end of Portal was evidence enough. Chell's fate, however, remained a wildcard until the aforementioned update. Previously, we saw Chell catapulted to freedom following GLaDOS' demise. Assuming she avoided any grievous injures, her escape was fathomable. Now we know better. She's back in captivity one again.
One new detail complicates Valve's carefully implemented continuity - Portal 2 takes place hundreds of years after the original game. We assume the party associate stashed Chell in some sort of stasis chamber in which she's quietly passed time.
While Chell appears relatively unscathed, the Aperture Science facilities haven't fared as well. Centuries after the explosion, no one has been around to repair sprawling campus. Overgrown areas are interspersed with cold and clinical test chambers, now in various stages of decay. As far as we (and Chell) can tell, no one has stepped foot in the derelict labs for decades. But loneliness won't overtake you, as a cast of slightly less organic characters has thrived in GLaDOS' absence. At the end of Portal, illuminated by a candle atop the tabled cake, rows upon rows of personality cores were awakened. These spheres are the same as those Chell ripped from GLaDOS' breast as she incinerated her captor one piece at a time. Introducing this new "species" allows Valve the chance to integrate unique AI personalities without introducing human peers. It also addresses the concern that returning to an isolated GLaDOS and Chell relationship would feel too much like a retread.
Migrating from their sublevel confines throughout the centuries, these spheres have carved out sections of the neglected facility as their own. Wheatley, one such personality core, proves to be the perfect tour guide to lead us through our first glimpse of Portal 2 gameplay. Concerned about the buildings deteriorating conditions and tired of his limited mobility (personality cores are appendage-less and thus confined to rails on laboratory ceilings), Wheatley ponders his odds of surviving a jump from his lofty position, ultimately deciding that he wouldn't go unscathed. Instead he awakens Chell from her slumber and propositions her for help. Promising to share his knowledge of an escape route, Wheatley hesitantly puts his faith in Chell to catch him. His fears become justified when Chell fails the simple task.
Quick to forgive - and fueled by self-preservation - Wheatley navigates Chell throughout the facility from his new station in her hands, all the while blabbering incessantly. He proves useful for more than a laugh, however. Chell can plug Wheatley into various ports throughout the labs, allowing him to access the mainframe and bypass obstacles. Wheatley's a bit gun-shy, though, making clear that he can't perform with Chell watching.
As the duo make their way through the defunct facilities, the extent of the damage becomes clear. Debris often blocks the path as they traverse a massive cylindrical room populated with breaker switches. Here Wheatley warns that only the switch to power the escape pod should be flipped - or else. When Chell can't spot the switch amongst hundreds, she instead pops Wheatley into another port so he can do the dirty work himself. Almost instantly, the neglected equipment malfunctions, and the floor below them reveals itself as an elevator that begins ascending, flipping all the switches on the periphery in the process. Acutely aware of the damage that's been done, Wheatley scrambles to find an abort password, forgoing a practical algorithm for a sequential brute-force strategy. "AAAAAA? No. that's not it. AAAAAB? No? AAAAAC? You've got to be joking!"
The climb halts as the platform comes flush with the door of a chillingly familiar location: an overgrown courtyard now housing the soulless shell of GLaDOS. Having no luck with the password, Wheatley trembles in fear at the first rumblings of a returning foe. We all knew the GLaDOS-less respite wouldn't last long. Slowly reborn in a bath of sparks and debris, GLaDOS awakens. Recognition crests immediately.
"...Oh, it's you," accuses GLaDOS in the throaty, sultry voice she first slipped on at the end of Portal. She continues, punctuating each short sentence with a drip of venom. "It's been a long time. How have you been? I've been really busy being dead. You know...after you murdered me?" Collecting her thoughts with another brief pause, an exaggerated and very human exhalation follows. The menace dissipates and she carries on. "Okay look, we both said a lot of things that you are going to regret. But I think we should put our differences behind us. For science. You monster." The short exchange is chilling, even after GLaDOS makes it obvious that she's more interested in resuming your relationship than revenge. With Chell once again a pawn in Aperture Science's grasp, the tests recommence. Even though the playing field is drastically different this time around, the odd couple falls back into routine like old lovers.