Olivia asks who else knows about this, and Peter says nobody: "I worked for him for years, and I didn't even know," adding that it's why he was willing to die so Walter could live. Peter unbuttons his shirt oh -- it's that kind of party, is it? -- and unlocks a heart-cabinet on his chest. Inside is the glass heart, beating merrily away. "It's your heart," says Olivia. Peter says he was born with it, and he was willing to give it to Walter because of all the good he's done, at least until he learned the truth: "Walter Bishop isn't responsible for all the goodness in the world. But he is responsible for so much evil."
Suddenly the house rattles and rumbles, and then busting through the wall is the little subterranean torpedo/vibrator we saw way back in "The Arrival." "Oh hell," says Peter. "They found us." And then the house is overrun by Observers, er, Watchers. It's a royal rumble of sharp-dressed baldies! After some hand-to-hand combat, which the Watchers look like they're losing, despite their superior numbers, one of them pulls one of those freaky guns and starts firing at Olivia, chasing her through the house, until at last she's able to grab one herself and start firing back.
And just like that, the Watchers are gone. Like not repelled, but suddenly not there anymore. She heads back to the living room, where she finds a tired-sounding Peter sitting on the floor. "I knew you were a good dancer. You really cut a rug out there," he says. "Well, you're not so bad yourself," she tells him. She opens the heart-cabinet on his chest. It's empty. "I need your help, Olivia. I'm dying."
After the commercial break, Olivia scrabbles through drawers to find some batteries, like you'd think she needs new batteries for her Wiimote or something, and asks Peter what she does now. "Well, you ever play that game Operation?" says Peter, struggling to breathe. He tells her it's just like that, only in reverse: "Whatever you do, don't touch the nerve endings."
She's extremely nervous, and Peter has to grab her hands to steady them and tell Olivia that she's going to be fine, and to take them one at a time. And while Olivia gingerly pulls out the battery connecters, Peter chats her up about why she became a detective ("To care for people." "Then who cares for you?") so I guess it's a good thing that the Watchers didn't steal his glass balls.