Few days after she defeated Wheatley, in mysterious circumstances Chell decided that she want return to Aperture. Right after she entered the building, she passed out.When Chell woke up in a long-term relaxation chamber, she discovered that someone turned off the Artificial Intelligence. From this moment, Chell have to pass test chambers, if she wants to stay alive.On her way, she finds out more information about "GLaDOS" , and the new "Aperture Science" .
I guess it's requires more work.