Meredith's half-sister, Lexie, attempts to bond with Meredith, who remains resistant to having a relationship with her.

Jane Burke returns to the hospital to collect her son Preston's belongings following his departure. Cristina, meanwhile, begins trading her unwanted wedding gifts for surgeries and favors from other doctors.

The residents and interns treat victims of a massive apartment fire caused by a meth lab explosion. Alex Karev deals with a particularly difficult case involving a baby who suffered a stroke due to the meth lab environment.

Watch a recap of the episode's themes and major character developments here:

George struggles with his guilt after admitting he loves Izzie, while Callie, as Chief Resident, is overwhelmed by her duties and her suspicions that George is cheating.

The episode explores various forms of "addiction"—from chemical dependency to toxic emotional attachments—as the staff at Seattle Grace Hospital treats victims of a massive apartment explosion. Main Plotlines

is the second episode of the fourth season of the medical drama series Grey's Anatomy .

Meredith and Derek continue their "friends with benefits" arrangement, which Derek eventually admits feels more like an addiction than a healthy relationship.