More tattoos? Yes, Will, Christina, and Tris have got new tattoos. Tris's tattoo this time is of the Abnegation symbol.
After that, Tris tosses some Erudite articles about Abnegation ("I hear they kick puppies!") into the chasm with Will and Christina.
But then she sees Four and follows him to the fear landscape room. And he invites her into his fears so she can learn about him. Which is kind of like sneaking a peek at someone's therapy records. Super personal.
So what does Four fear? (1) Heights. (2) Small spaces (because he used to be locked in a small closet as punishment when he was a kid). (3) Shooting a woman. How very chivalric. (4) And his abusive father, who is… Marcus, the Abnegation leader who works with Tris's own dad.
Which means that Four is actually Tobias, the son who left (that we heard about in chapter 4).
That means Four was bourn into an Abnegation family, but transferred to Dauntless.
While she's mind-melding with him, she helps him get out of all these fears, including this last one, where she gets in between Marcus and Four/Tobias. (Get it? He's called Four because he only has four fears.)
But Four has one more thing to show Tris… that we'll learn in chapter 26.