Meredith nearly loses her lunch when Derek’s wife, Addison, shows up at the hospital. It’s worth noting that Mer didn’t even know Der had a wife. D’oh!
Izzie pulls some unethical strings to get Denny a new heart, but he dies in her arms anyway. She later quits her job. Meredith, meanwhile, is forced to choose between Derek and Chris O’Donnell.
Burke calls off his wedding to Cristina, George fails his intern exam and Derek and Meredith break up.
Meredith surprises Derek by laying out the blueprint for their dream house in candles.
George, fresh off getting flattened by a bus, and Izzie, fresh off a cancer relapse, are knocking at death’s door in the final moments of the episode. (George would later die.)
A crazed gunman goes on a shooting rampage at the hospital, killing Dr. Percy and Adamson and severely injuring Derek.
Owen breaks up with Cristina after she insists on aborting their baby. Derek threatens to walk out on Meredith in the wake of her Alzheimer’s trials tampering just as Zola comes into their lives.
Meredith, Derek, Lexie, Cristina, Arizona and Mark fight for their lives after their plane crashes in the middle of nowhere. (Lexie and Mark would later die.)