George and Derek work together, Denny still doesn't have a heart, and Meredith gets paired with Callie. A 12-week pregnant girl dies in the O.R. and her parents try to keep the baby alive. This causes tension between Derek and Addison. One doctor's overreaction unites two bickering patients. Finn is still treating Doc for medical problems.
 Expanded overview
A shooting at a nearby restaurant bombards the hospital with plenty of gunshot victims -- and one intended victim that didn't get shot, but is a pain to everyone nonetheless. Burke is still mad at Christina, and he lets Alex go with him to retrieve a heart and not her. Cristina winds up on the case of a couple where the boyfriend used his girlfriend as a shield during the shooting. When Izzie finds out that the heart is for Denny, she begs Bailey to be on the case, so she can tell Denny the good news and prep him. Meredith works with Callie on a victim who was shot in the leg. She uses the time with Callie to pick her brain about bone cancer in her dog, but Callie doesn't have time for any dog talk -- until George says he has a right to be mad at Meredith, but Callie doesn't. George and Derek attend to a victim left brain dead -- and pregnant.
Derek seeks Addison's help in talking to the parents about their decision to use their daughter as an incubator, but Addison -- who is seething to find out that Derek and Meredith's strife extends from Meredith dating the vet -- explodes on Derek in full view of everyone. When the heart intended for Denny doesn't prove to be viable, Burke fights for a second heart that is supposed to go another patient in another hospital -- and it's a battle he's losing until Izzie decides to take matters into her own hands. As Burke races back to SGH to keep Izzie from stopping Denny's heart, both Burke and Denny wind up in critical situations.