Peter's shaking because he doesn't really want to do it, but the moment's about to pass anyway. Walter says, "Forgive me," and shoots Olivia in the forehead! Which deserves probably more exclamation marks than I'm comfortable handing out! Can't say I saw that coming! I mean, it's not like even now I had any concern that Olivia was going to stay dead, but at least Walter shooting her was a surprise. "Noooo!" shouts Peter and he rushes to Olivia's crumpled body.
Outside, the ship snaps from the other universe back into the clear skies of ours, with the three helicopters circling overhead desperately hoping that the prevention of Armageddon doesn't rest solely on their shoulders.
Inside, Peter cradles Olivia's head and yells, "You killed her!" at Walter, who turns his gun on a surprised -- and impressed -- Bell. "If that's what you consider learning a lesson from the past..." he says, and rings the ship's bell, "...you paid a steep price." We had one of those in the university bar where I bartended. If someone rang it there, they had to buy everyone a drink. Here, it makes Walter shimmer out of sight. "We could have all been so happy together," he says as he disappears. "You killed her," whispers Peter, hugging Olivia's lifeless body.
After the commercial break, Walter tries to step in, but Peter angrily tells him not to touch her. "We have to move rapidly if we're going to save her," says Walter. Peter points out that she's dead and Walter has to remind him that that means much less on this show than it does on most others. He slaps Peter to get his attention and then directs him to Bell's desk, telling him to get the letter opener and to clear everything else off it.
They lay her body down, and Walter explains that Olivia's brain is saturated with Cortexiphan, making it regenerative, so if he can get the bullet out before the Cortexiphan wears off, he'll be able to save her. "It's like my lemon cake that was so conspicuous by its weirdness as it introduces a heretofore unknown side effect of Cortexiphan last episode," says Walter.