Gary Clark returns to Seattle Grace to seek revenge for his wife's death. He goes on a shooting rampage and shoots Reed in the head. He then shoots Alex then goes to find Derek, who he feels is responsible for his wife's death. Alex tries to get on an elevator but is not able to go down.
We find out that Meredith is pregnant. Meredith meets Christina and tells her;) Christina asks Meredith if that is a good thing, and she nods. She plans to tell Derek but when she tries to tell Derek, he seems busy. So she decides to tell him back at home.
The hospital goes on complete lockdown. Meredith and Cristina find themselves in a supply closet, waiting for all the commotion to be over with. Lexie and Mark find an injured Alex collapsed on the floor and they try to help him.
Dr. Bailey and Dr. Percy are with a patient named Mary, played by Mandy Moore. Gary bursts into the room and immediately Mary plays dead. Dr. Bailey successfully hides under the bead, but Dr. Percy is not so lucky. He gets shot as he aggravate Clark by saying out he is a surgeon. Callie and Arizona are in the Pediatric section of the hospital. Owen, Teddy, and Jackson are operating on a patient in the OR, and are told to stay. Meredith finds out that Gary is looking for Derek. She runs out to find him, but Gary gets to him first, and Derek is shot.