The day's rounds require that George (T.R. Knight) team up with Derek (Patrick Dempsey)--and, less harmoniously, that Callie (Sara Ramirez, now a series regular) team up with Meredith (Ellen Pompeo). In other developments, Finn (Chris O'Donnell) gets an update on the wellbeing of Meredith's dog Doc; Denny (Jeffrey Dean Morgan) is all primed for the transplant, but the donated heart suddenly becomes unavailable, forcing Izzie (Katherine Heigl) to take drastic measures; and Callie has something very important to say to George. The episode comes to a shocking climax as Burke (Isaiah Washington is literally laid low by an unexpected catastrophe. ~ Hal Erickson, Rovi