Olivia starts to move to go after him, but Peter is all "I got this" as he stops her and goes after Walter himself. That's when Olivia notices, on the bedside table, a little radio.
Meanwhile, poor Astrid is just standing around, waiting for the rest of her so-called teammates, not even really knowing if they're alive or dead. She looks out a window and sees that the Observers and Loyalists are rolling in. Outside, Windmark tells everyone that search parameters remain the same: building to building, door to door. And if you find any corpses, check them quickly for antimatter batons!
Back in the pocket universe, Peter has found Walter -- not exactly a given, considering where they are, so nice job running off, Walter -- and he's crouched on the floor, being all crabby and sulky.
Peter crouches down himself and points out to Walter that if the Observers had known about this pocket, they would have shut it down long ago: "The only person other than you that knew this place existed and how to navigate it is Donald," he says, and Walter, sounding a little hopeful admits that makes sense. But he hasn't figured out why he would move the boy. That's going to be tough, to figure out Donald's motivation when you don't even know WHO DONALD IS. Peter points out that they were missing for a long time, so maybe Donald thinks Walter is dead. Walter has no idea who he is, where he met him... anything. "We have to find him. Donald, whoever he is. It's the only way we'll ever know for sure," says Peter. Olivia pops by to tell the Bishops she think she's got something, and Peter takes his father's hand and helps him stand up.
They look over the video footage of the room again and Olivia points out that the radio is nowhere to be found; she thinks whoever took the boy left it behind. Walter takes it and fiddles with it, and then declares that the batteries are dead, and Olivia has to remind the super-genius that, as with the video camera, things work differently here, so maybe they need to get it outside.
Walter brightens up considerably and calls Olivia "brilliant" because obviously if he missed it then one has to be "brilliant" to figure it out, and he hypothesizes that perhaps it will somehow help them get to Donald. "Assuming he's still alive," he adds.
Peter suggests it's time for them to get out of there and Cecil's all, "Please," like shut up, Cecil, you're bringing nothing to the table here.
Meanwhile, Astrid's watching the enemies pile up outside -- "Come on, guys," she whispers -- and then she's suddenly got a bigger problem: An Observer pops into view right in front of her, and he backhands her, knocking her to the ground, unconscious. Another one pops in and they look around the room. We get special Observo-vision, where the room is rendered in bright blue, with shimmery streaks of light and blurriness around the entrance to the pocket universe. They step through it and disappear from our universe. At this point, I'd like to remind everyone that Walter said this pocket universe is undetectable to Observers' instruments, but I guess he didn't account for them LOOKING AT IT.