The fine ladies and gentlemen in Bureau of Genetic Welfare turn out to be the puppet masters of the Chicago experiment. All those cameras are connected to them. They're the Big Brother of the Divergent world. The scary thing is that they're not just monitoring Chicago; they're also monitoring people on the fringe, people who are supposed to be free. Who won't these people monitor?
Well, as readers, we get to monitor them for a change, and we have a few things to say.
One of the first members of the Bureau we meet is Zoe. She's the least interesting member of the group. She gives Tris a photo of her mom and, later, she gives Tris her mother's journal, but Zoe has no personality of her own. We don't even know what becomes of her in the end, after everyone's personality is erased (maybe because she has no personality to erase?).
A couple of people come back from the dead, but not in a Walking Dead way—more in a faked-their-own-death-like-Elvis way. Tobias is reunited with his Dauntless trainer, Amar, who is in a chaste homosexual relationship with Tori's not-dead brother, George. Hey, at least they're getting a little same love off-page, unlike poor Lynn, who died in the last book.
Matthew the lab tech and Nita, his assistant, become objects of jealousy for both Tris and Tobias, even though neither one is interested in the other romantically. Nita is actually very similar to Tris: she wants to bring down the Bureau and create a better world. Matthew is also a lot like Tris. He's working with Nita (even though he doesn't agree with her whole kill-them-all assassination plot) because he despises the injustices perpetrated by the Bureau. Like Tris's mother, he lost someone close to him because she was genetically inferior.
Finally, there's David, the leader of the Bureau. When something goes wrong with the experiments, he simply wants to reset everyone using the memory serum, wiping out the memories of thousands of people to just… start over. He ends up in a wheelchair after he's caught in the middle of a gunfight between Nita and Tris, who uses him as a human shield, but that doesn't stop him from attempting to lead the Bureau. And by "lead" we mean "totally give up and just brainwash everyone into agreeing with him."
It's pretty appalling that he's willing to pretty much erase everyone's existence just because the "experiment" is getting out of hand. You'd think he'd be a little more sympathetic to the people in the city, because he was in love with Tris's mom, who volunteered to be one of his precious "experiments." When Tris blames him for her mother's death, he shouts that he's not responsible (50.16). We think he's protesting too much.
David actually shoots Tris right as she releases the memory serum. The bad news is that he kills her. The good news, at least for him, is that he doesn't remember killing her, because she succeeds in unleashing the memory serum and erasing his memory. Tris observes early in the novel that if you "take a person's memories […] you change who they are" (12.20). But is David a different person at the end of the novel? Is erasure an appropriate fate for him, or do you wish he'd have suffered a little more for his actions?