Olivia looks stricken. She gets on the phone to tell Walter the bad news, and he's so bummed out that he won't even tell Astrid what happened; he just goes into his office and closes the door. Aaron, strapped into Walter's god-awful headgear, watches him.
In the Hyde Park tunnel, the soon-to-be-dead Massive Dynamic technician says they're looking for a central mass to best distribute the toxin. He finds it, and gets out this giant injection apparatus with a five-inch needle at the tip. He readies it, and then waits, telling Olivia he was told it was on her order. Olivia waits a moment, and then says OK. The tech jams the needle in, and the pushes down the huge plunger.
In Walter's lab, Aaron sits up and yells "no!" And back in the tunnel, a tentacle-like tendril has shot out into the technician's chest. Astrid rushes into Walter's office to tell him that Aaron's blood pressure is falling and he's lost consciousness. She wants him to do something. Walter has no idea what to do, and... OH WAIT! Now he knows what to do.
"The toxin's been administered but the technician is dead," Olivia tells Broyles. Hey, gotta break a few eggs to make an omelet, right? Broyles wants the two of them to fall back, but that's going to be a problem since Gus is wrapping some tendrils around Lee's legs.
In the lab, Walter's come up with one of those solutions that is completely out of left-field because it's the exact opposite of what he originally thought: first, the source of Aaron's distress isn't isolated in the pre-frontal lob, but also in the limbic system, the emotional centre of the brain. Want to surgically remove that too? He tells Astrid to get him some epinephrine.
Meanwhile, the fungus is really going to town on Lincoln Lee, and Broyles tells them that they're assembling a team now. What do you mean "assembling"? Shouldn't that have already happened? Anyway, the worse news is that Gus appears to still be alive.
Anyway, the other backwards part of Walter's hypothesis is that it's not the fungus that has a hold on Aaron, but the other way around. The link is emotional. Then Walter -- gah! -- gives Aaron a shot of epinephrine in the neck, and shakes the kid until he walks up, then starts yelling at him to let go of the organism.
Aaron says it's his friend, and he'll be alone. Walter tells him it's not real: "It's something that's invaded your mind. It's hurting you," he says, because it should go over great that the one friend the kid thinks he DOES have isn't actually real. His blood pressure is still falling, says Astrid, and his organs are shutting down. An emotional Walter tells Aaron that he cares, and he can't lose him. "Not again," says Walter. Again. And then he babbles on about how hard it is to make connections, what it means to be lonely, that sort of thing. He begs Aaron not to leave him, and I'm SO SURE WE'LL SEE AARON ON THIS SHOW AGAIN, and then he pleads with Aaron to let the organism go.