Modern-Day Sterling looks through Simon's file and notes that all the next of kin are deceased. And all his school transcripts are missing. And the pictures from ten years ago look exactly like him today. So he's willing to consider the possibility that Simon's one of Them. His plan is to check some blood and then start the Enhanced Interrogation. Which makes sense; unlike the Detainees (who just got thrown in jail for being suspicious), Simon's an actual spy.
Madeline has taken Leila and Sean to a building called "The Langham." There isn't a caption to tell us what part of the country we've been whisked away to. We were in Atlanta in the last scene, so I'm going to assume we're now in Minneapolis. It only makes sense, right? Madeline pushes the door buzzer several times until someone (bringing our Mysterious Man Count up to three) answers. He doesn't answer in person, of course; he's ensconced in a room somewhere behind multiple computer monitors. He doesn't want to let them in, but Leila brings up Samantha, and that's good enough to get them through the front door. When the mysterious man is in the same room as Sean, Leila and Madeline, he insists that they empty their pockets, because they're trackable. Or something. To the extent that he's talking about anything real, I think he's referring to RFID chips. Sean denies having anything like that, although he definitely has a mobile phone on him. It's kind of strange that a genius hacker would forget about his smartphone like that. Sean hands the notebook over to Mysterious Dude, who smugs at them about having "sources" in the Intelligence Community. And that means that he knows that Leila's father is being held by the government, although he thinks Samantha is probably dead. He clarifies that that's just a guess, which means he's just going out of his way to be unhelpful. Sean asks for "a few minutes on your system," because this show thinks if you put a superhacker on a computer, you can get away with anything.