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.

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

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