Teddy and Owen are finished with the surgery, and Owen wants Avery to take the patient up to ICU. But Avery can't do that because, as he announces, there's a shooter and a lockdown and an order from the Chief. Owen's pissed that Avery didn't say anything until now, despite what Derek said. Now they've got a hypothermic patient who needs to get warmed up in ICU lest he die. Owen decides to take him up to ICU himself. He balks when Teddy says she's coming too, so she had to play the whole "I'm a cardiothoracic surgeon and my patient has a penetrating chest wound" and blah blah, she's coming with him. (Also, sidebar: Penetrating Chest Wound! That's the PCW they keep talking about in this episode. You guys, there are a LOT of them.)
Callie and Arizona that one intern Graciella are dealing with this poor girl and her appendix. Arizona has Graciella set up a portable ultrasound, then rounds the corner for some supplies. Callie follows her, asking when she's gonna let her off the hook for "not being a good enough lesbian for you." Oh HOLY JEEZ, Callie, this is why people hate this show! Yes, it's also why people love this show, but come on, man! Eye on the ball! Arizona returns that she can't trust that she's any different, in Callie's big ol' heart, than George or Erica or Mark or the coffee cart girl. She can't trust her not to move on to the next thing, basically. This seems to quiet Callie's rage for a moment, and Graciella comes around and, not wanting to freak out the girl, just makes an exploding motion with her hands, re: the appendix.
Cristina and Meredith are having trouble cooling their heels in the supply closet. Meredith, in particular, is feeling the morning sickness she's been suffering from all week rear its ugly head. Cristina's like, "Yeah, I'm not gonna be able to be here with you and the pervasive smell of vomit, shooter or no shooter. Except: shooter. Because Cristina spots Clark walking down the hall right towards them. She whispers to Meredith to get out of sight, and we all start praying Mere can keep from vomiting and thus alerting Clark to their presence. Cristina gets a good look at him as he walks past their room, and she recognizes him as the guy from the elevator. Then she remembers that he was asking how to get to the Chief's office. It takes Mere a second, so Cristina bottom-lines it: "The guy with the gun is looking for Derek." Time for Mere to vomit!
After the commercial, Derek races across the catwalk when he hears a man call to him from behind. Mr. Clark, obvs. The gun's in his pocket, so Derek tells him to get out, that it's not safe. "Of course it's not safe," Clark muses, almost laughing. "That's the whole point. This hospital isn't safe." He asks if Derek doesn't recognize him, and right then, Derek does. He tells him to get someplace safe before he gets hurt. "I'm already hurt," Clark says as he raises his gun. "You hurt me when you decided to kill my wife." To Derek's credit, he doesn't say, "Oh. That."