Meredith's best friend from college shows up on her doorstep and Cristina feels threatened by it. Meredith thinks Sloan is putting the moves on her half-sister and asks Derek to intervene, while the interns practice sutures on each other and Izzie still feels Denny's presence. Hahn is suddenly gone from Seattle Grace and everyone immediately feel at odds over her replacement.
Cast: Ellen Pompeo, Sandra Oh, Katherine Heigl, Justin Chambers, T.R. Knight, Chandra Wilson, James Pickens Jr., Sara Ramirez, Eric Dane, Chyler Leigh, Patrick Dempsey, Jeffrey Dean Morgan, Kevin McKidd, Melissa George, August Schellenberg