Recap / The Courtesy Call

Opening the door, Chell is greeted by what appears to be a sentient morality core hanging from a ceiling rail that extends into the room. The core - named Wheatley - activates a crane mechanism that carries the room through what is revealed to be a massive dilapidated facility filled with "tens of thousands" of rooms like Chell's, before depositing it near a docking center to the Aperture Science Enrichment Center and instructing Chell to find "a gun that makes holes"...

Departing the room, Chell makes her way through a number of still-operational test chambers in various states of ruin, many of which she previously visited during her stint as an Aperture Science test subject. Along the way she obtains the Aperture Science Handheld Portal Device - the "gun" Wheatley had referred to earlier - before reuniting with the core himself, who disconnects from his rail to allow Chell to plug him into a socket within the wall, enabling him to open a side panel that grants Chell access to the inner workings of the facility. Carrying Wheatley with her, Chell continues onward, eventually reaching the remains of the chamber where she once faced off with GLaDOS. Thankfully the malevolent AI is still "out of service" following her showdown with Chell, but Wheatley accidentally reactivates her and the rest of the facility while trying to activate the place's escape pods, and GLaDOS wastes little time before grabbing both him and Chell. Tossing Wheatley away, GLaDOS reveals her intent to subject Chell to more tests, before dropping her down the tube Chell once used to dispose of her personality cores.

Landing within the incinerator room of the facility, Chell acquires a dual portal version of the Aperture Science Handheld Portal Device, and uses it to travel through the ruined facility. As she does so, GLaDOS reveals that she has been stuck reliving the last two minutes of her life - i.e. her "death" at Chell's hands - ever since her previous defeat, but she claims she's not mad with Chell about that. After all, there's little point in that considering all the tests they're going to do...