Wheatley eventually helps Chell escape the test chambers. Together, they sabotage GLaDOS's turret and neurotoxin production lines. They confront her in the central control room and perform a "core transfer," replacing GLaDOS with Wheatley.
They return to the modern facility to find Wheatley has made a complete mess of things, pushing the reactor toward a core meltdown. In the final battle, Wheatley booby-traps the room, but Chell notices the roof has been torn open, revealing the night sky.
Portal 2 is a direct sequel that expands the lore of Aperture Science, taking place centuries after the first game. Below is the complete narrative arc of the single-player story. The Awakening and GLaDOS's Return