Michael's first expression isn't shock; it's a sad confirmation. (I think he had suspected something, and Linc finally admitting the truth only strips away the hope Michael had that he was wrong.) As Linc chokes out, "I lied to you. I'm sorry. If you don't break out today, they're going to kill my son," Michael stays silent, tearing up, trying to pull himself under control. Then he walks off as Linc shouts, "They're going to kill L.J. Michael, we've got to do this! Michael!"
And then we get a montage wherein Michael flings himself around the prison in a tremendous display of grief. It would be a lot more touching if it weren't given the musical-overlay-and-arty-transition business, but that's okay. I can see how devoting time to the protagonist's reaction upon hearing the news would totally drag down the story. It's not like Michael had a really intense emotional thing with Dr. Sara for two seasons, so why waste time exploring his reaction?
When we finally get out of the montage, Michael is walking down the steps and back into the courtyard, totally numb. He approaches Whistler and says, "Sara's dead." Then he looks stunned, as if saying it aloud made it even more real. Whistler turns to look at Michael, and Michael adds in a raw whisper, "They killed her." "I'm so sorry," Whistler responds. He walks off and Michael follows, saying, "I loved her." And you know, I really like how Wentworth Miller's playing it here and I think that the writers kept Michael's reaction true to character, but here is my quibble: loved? As in past tense? Within minutes of hearing about Dr. Sara's death? I'm thinking he's still in the present tense emotionally.
Anyway, Michael has decided he blames Whistler for Dr. Sara's death. Whistler turns around all, "What?" and Michael shakes off his hand. We get a shot of Bellick suddenly paying attention to proceedings. And then, we see that Lechero is now standing next to Michael. Michael sniffles and whips out the chicken foot. Whistler is all, "Wha...huh?" Michael whispers, "This is your fault?" Whistler seems genuinely baffled. Lechero says, "He's told me his grievance. This fight is going to happen." And Lechero's looking pretty thrilled about that. Whistler makes a last ditch effort, exhorting Michael, "Just think about what you're doing!" Michael snarls, "I have!" He slams the chicken foot on the ground, and all the inmates in the courtyard cheer. The episode ends with the mob cheering, Whistler looking baffled, and Michael attempting to kill him through the power of Blue Steel.