Meredith's half-sister, Lexie, attempts to bond with Meredith, who remains resistant to having a relationship with her.
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. [S4E2] Love/Addiction
Watch a recap of the episode's themes and major character developments here: as Chief Resident
Meredith and Derek continue their "friends with benefits" arrangement, which Derek eventually admits feels more like an addiction than a healthy relationship.