Ah, Seattle. Home of the Space Needle, Pike Place market, the flagship Nordstrom and, apparently, crazed gunmen who like to shoot up a lot of innocent bystanders in one go. Cristina, fresh off of her cathartic fishing trip, decides to take a walk and explore the city but when she sees a line of ambulances scream by, she follows them and comes to a college where a gunman has shot down at least 20 people. She watches the paramedics load one kid into an ambulance and realizes that they need to crack the kid's chest, but they don't seem to be doing it. This seems to be the nudge she needed in the right direction, so she does it herself and plugs up his torn artery with her finger. Owen and Teddy are shocked to see her when they open the ambulance door, but they go with it and she tells Teddy she wants to stay and help with the surgery. When it turns out later that the kid they are working on is in fact the gunman, Jackson decides he can't help anymore, but Cristina decides to stay and seems to be back to her confident, ass-kicking ways.

Everyone at the hospital is understandably distraught about the shooting, some more than others, but it also makes them more able to understand and help the victims and their friends and family. Derek's way of dealing with things is to turn into a jerky surgery robot, and he insults Meredith for repeatedly leaving to update their patient's panicky wife about the surgery. She finally lets him have it by reminding him that she went through a trauma, too, not just him and Cristina, and that being the wife in the waiting room is so hard it caused her to walk in and tell the gunman to shoot her. She storms out and thankfully, it snaps Derek back into being a human again, he apologizes to all of the staff in the OR, and continues with his job. It's a tricky surgery, but the guy survives.

Once the ORs are all full, Owen turns the pit into a makeshift surgical area and puts April in charge of running the place, since she "won" his trauma clinic a few weeks previously. She's able to do it, and she, Bailey, Richard, Lexie, Mark and eventually Alex all work away on their patients down there.

Alex started out the day in one of the operating rooms with Stark, but when Stark decides it's easier to amputate the girl's leg rather than put in the extra work to save it, Alex yells at Arizona, up in the gallery, to intervene. Arizona thought she'd come right back to a girlfriend and a job in Seattle but the Chief had told her he didn't have the money to buy out Stark's contract, and Callie has no interest in talking things over. However, with all of the action, the Chief gives Arizona privileges, so she throws on scrubs and runs into the OR (where Alex has awesomely been putting his wrestling skills to use by physically blocking Stark's path to the patient) and takes over. She has Callie come in to work on the leg and thinks this might be a way to talk to her very angry ex-girlfriend, but Callie is having none of it. They save the girl but Callie tells Arizona that it doesn't mean anything and she still wants nothing to do with her. Fortunately for her, the Chief is more of a softie than Callie and tells her he'll hire her back, though she'll have to work under Stark... and it's not entirely clear if he's joking or not.

After everyone finishes up tending to their patients, they all wind up in the gallery watching Teddy and Cristina work, and Richard congratulates them on saving all of the patients that came through their doors that day. Afterward, Mere finds Cristina and OH HOORAY they actually say hi and seem to slip back into being friends. As they are reuniting, so are Lexie and Mark -- while he works on cleaning up the sutures on a patient, she tells him that she loves him.

Teddy doesn't hang around the hospital when she's done operating but instead goes to Joe's, where she meets up with her new husband. Oh yes, you heard me right -- she really did marry Henry that morning, and she has the insurance paperwork for him to fill out. While she's incredibly down from having just spent the day operating on a would-be mass murderer, Henry is of course charming and awesome and cute, and manages to convince her that she also saved his life that day. Yeah, those two are totally falling in actual love sometime.