Below, in the hot box, Dickhead wheezily pleads with Doggett not to abandon him. Doggett gives him a dirty look, but helps him up. As they limp down the tunnel, Doggett spies the mysterious "other person" for whom they had been searching, and calls out that whole "federal agent/halt!" rigmarole. Scully watches open-mouthed as Doggett closes in on what turns out to be a child. He and Scully both make amazed faces. The kid doesn't respond to any of Doggett's questions, but just points and gestures. Scully has Doggett turn the light away from the child, so that she and TaeBo can see that the lovable scamp is uninfected. "How can that be?" wonders TaeBo. The proverbial light bulb goes on over Scully's head, as she realizes what the rest of us figured out half an hour ago: sweat triggers the reaction. She spits out some science stuff that boils down to the fact that sweat conducts calcium ions, and that kids aren't as sweaty as grown-up folks. Doggett absorbs this information as the kid gestures for him to follow him into a small room.
Doggett leaves Dickhead and trails the kid, finding a room which he calls "the source of the contagion" -- the room where the leak originated. Water from the bay is trickling in, coating the walls and the floor. The kid splashes through the room, still gesturing for Doggett to follow. Scully looks at her map and tells Doggett that the kid appears to be leading him into an active line, about four hundred yards from an "access point." If he can get to that point, she tells him, she can get him out in roughly fifteen minutes. Doggett goes back to fetch Dickhead.
They lurch through the contaminated room, and out onto the main system, which Doggett notices has also been contaminated by the Evil Ocean Water. Scully sighs that they have bigger problems than that: there's a train heading right for them
Drums of Impending Doom. Doggett drops Dickhead to go investigate. The subway is, yes, heading right for him. Scully yells at Doggett to get off the tracks! Doggett yells that people on the train will get infected! Scully yells at him to save himself, man! Doggett ignores her, and gestures to the kid to hand him something, which he does. I can't tell what it is, thanks to the damned atmospheric lighting. Whatever it is, Doggett -- like some kind of twenty-first-century MacGyver -- in the space of, like, two seconds, manages to use it to create an electrical-type explosion between the water and the live third rail, and also somehow jumps out of the way of the oncoming train right in the nick of time.