Meredith tells Cristina that she’s pregnant. But despite this happy news, something bad is going to happen

Sure enough, the disturbed Mr. Clark comes into the hospital and shoots Reed in cold blood.

Then he shoots Karev!

Alex crawls away towards the elevator, leaving a trail of blood.

Meredith tells Derek she has some news for him. She also promises "lots of dirty sex." He is buried in paperwork and doesn't get it.

Cristina confronts Owen - does he love her or Teddy? He hesitates. She’s done.

Gulp. Cristina gets in the elevator with the shooter. She gives him directions to Derek’s office, not knowing she’s aidind a psycho.

The first body is discovered and April has a complete freak out. Derek locks down the hospital. Meredith goes to see Cristina.

They talk about Meredith being in a new, family woman. Then Cristina tells Meredith her news - she’s broken up with Owen.

Elsewhere, the shooter opens fire in a crowded part of the hospital.Karev’s body is discovered in the elevator. Mark and Lexie try to save him.

Cristina and Meredith continue to talk about their love lives, unaware of the chaos that’s broken out elsewhere.

As Bailey works with her patient, played by guest star Mandy Moore, the shooter comes in. He shoots Percy when he says he's a surgeon. Then he asks Bailey if she's a surgeon too. She says she’s a nurse and he leaves.

Callie and Arizona talk about their love lives, still unaware of the chaos. Bailey works to save Percy.

Meredith and Cristina are hiding in a closet and see the shooter. Cristina realizes he’s going after Derek.

Derek runs into the shooter in the hallway. He recognizes him as Mr. Clark, the disgruntled man whose wife was a patient the doctors “unplugged.”

Clark says Derek hurt him when he let his wife die. He starts to talk the guy down, but another doctor interrupts and Clark shoots Derek.

The SWAT team moves in — and Meredith moves out of the closet to help her man.

Meanwhile, Richard waits outside the hospital, helpless. The whole place has been locked down.

To be continued in "Death and All His Friends" ...