Tris wakes from a bad dream to find that the word "Stiff" is spray painted across her mattress in red, and written smaller along the bed frame and on her pillow. It's pretty obvious that Peter was the one who did it. Al helps her clean it up, and expresses his sorrow that he'll be known as the first guy who knocked someone out during initiation, even though Will isn't angry about his defeat.
When they go to training, Tris gets a shock: her first opponent of the day is Peter. Al suggests she take a few hits and pretend to go unconscious. Tris starts thinking about Peter's weaknesses, one of Four's strategies, but she realizes he doesn't have any. During the fight, Peter goads her on before laying into her. While she's being pummeled, she sees Four get up and walk out. The last thing she hears is "enough!" before she's knocked out.
Tris wakes up in the hospital to see Christina holding an ice pack to her jaw as well because Will managed to beat her up. Tris recalls the first time she was in the hospital at six years old, when her mother fell and broke her arm. An Amity nurse set it, and Tris remembers Caleb telling her it would mend quickly because it was a hairline fracture, and she wonders if this was his secret Erudite studies showing through.
Christina informs Tris that they'll be going on a field trip to the city fence the next day to learn about Dauntless jobs. Al hangs around Tris's bed for a minute and admits that he has begun to purposefully lose fights because he doesn't want to hurt people. Tris insists that this doesn't make him a coward, but he doesn't believe her. They discuss the approaching Visiting Day, during which families of transfers are allowed to visit their children one more time. Tris doubts her family will show up. That night, she slips back to the dormitory, so Peter won't have the satisfaction of putting her in the hospital overnight.
When Christina wakes Tris the next morning she's aching everywhere, and she struggles to get dressed and ready. Jumping onto the moving train is extremely difficult for her, but with Al's assistance she makes it. Christina and Tris discuss what is beyond the fence; Tris wonders what they're guarding the city from. They note that Dauntless guards weren't placed on the city outskirts until a few years before, after Tris's father and the rest of the Abnegation council voted to remove them from their positions policing the factionless.
They approach the fence, and Four explains that if they aren't in the top five at the end of initiation, they'll probably end up as fence guards. After inquiring, they learned that Four was ranked first in his initiate class, and even though he could have gotten a government job, he chose not to. Tris thinks about the very few options available to Dauntless members where jobs are concerned, and realizes that because her rank is so terrible she'll probably have last pick even if she makes it past initiation.
At the gate, the Dauntless guards open the doors to allow an Amity truck to pass, and Tris sees Robert, a friend from Abnegation, who transferred to Amity. Robert hugs her in greeting, which makes Tris stiffen, and Molly makes fun of her for her real name, Beatrice. Robert insists that Tris could go home to Abnegation if she wants to, if she isn't happy, but Tris refuses and says she chose this. As Robert leaves, she notices that the gate's lock is on the outside, as if they're trying to keep them in, rather than keep something out.
Four warns her against conversations like the one she had with Robert, and gives her advice for when she fights: attack first, because she's fast, and get a few hits in to take her opponent by surprise. She calls him out for leaving her fight in the middle, and he responds that it wasn't something he wanted to watch.
For the next training fight, Tris is luckily paired with Myra, who she beats easily. She's settling down to go to sleep when all of the sudden a group of Dauntless including Four and Eric wake them all and announce that they're going on another field trip. They are all told to grab guns containing paintballs, and once they board the train, Four tells them they'll be dividing into teams and playing capture the flag, a true Dauntless tradition.
He and Eric are the team captains, and the first person Four picks is Tris. He tries to convince Eric he's picking the weaker members, but Tris realizes he's picking people with small, fast body types, because capture the flag is a game of speed. Eric is cocky that his team of brawn will win.
Four's team goes to place their flag at Navy Pier, following the strategy of Four's winning team during his initiation. Navy Pier, once a bustling tourist attraction Lake Michigan, is falling apart in disrepair, and the lake has turned to marsh. Everyone begins arguing over the best strategy to take, offensive or defensive, but Tris decides that before they do anything they need to figure out where the other team is, and to do that she needs to climb to higher ground.
She sneaks off to the ferris wheel, but Four follows and insists on climbing up with her. On the way up, he asks what she thinks the purpose of this game is, and she suggests learning strategy and teamwork, but adds that teamwork doesn't seem to be a Dauntless priority as of late. Four laments that it used to be. When Tris's legs begin to shake, she at first thinks it's because of the height, but then realizes that it's Four's presence; he makes her feel like she's about to fall, or turn to liquid, or burst into flames.
Four asks what she thinks strategy has to do with bravery, and she says that it prepares you to act. Four begins to have some trouble; he seems to be deathly afraid of heights. When Tris asks how he survives in the Dauntless compound given the Chasm, he says he's learned to ignore it when making decisions. They continue to climb until the reach the top. Tris spots where the other team is hiding their flag. On the way down, though, Tris slips and hangs off of the wheel, dangling in midair. Four figures out a way to make the wheel work again, and she rides it to the ground before she slips to her death.
They tell the rest of their team where to look for the other flag, and they go running off to get it; when Tris and Christina reach for the flag at the same time, Tris allows Christina to take it and have some of the glory - though it is extremely difficult for her. Basking in their victory on the way back to the compound, Tris officially meets Marlene and Uriah, two Dauntless-born initiates, who compliment her strategy.
Contrary to what she believes, having an enemy like Peter really does bring out the best in Tris; he is quickly becoming the novel's most apparent antagonist for the time being, and all the work she puts into combating him brings out the Dauntless qualities that she needs to cultivate in order to make it past initiation. Though he physically bested her during their fight, the beating motivates Tris to do better next time, and this tenacity is a huge part of her character. In addition, her loss reminds her and the readers that she isn't home free yet. Despite the attention she got from being the first jumper, she still has a long way to go these next few weeks.
Tris's encounter with Robert accentuates the faction divisions that are ever-present; though all children from all factions were allowed to attend school together before Choosing Day, as initiates and official faction members they are kept apart. A good question to keep in mind while continuing to read is whether the factions have always been this divided, or whether friction has magnified over the years, just like Dauntless's gradual shift towards a more ruthless kind of bravery. That Tris isn't even allowed to exchange a few words with a childhood friend without falling under scrutiny shows how heavily present these divisions are, and how absolute that choice they made on Choosing Day is.
There's a bit of foreshadowing here when Tris notices that the lock is on the outside of the gate, rather than the inside; though she dismisses her suspicions as nothing, it would be wrong of us as readers to do the same, because it would not have been mentioned if it did not mean something. Are the factions really being kept isolated from the outside world for their protection, or for some other reason? This is another question to keep in mind throughout the rest of the novel, as the world unfolds for both Tris and the readers.
Chapter 12 is an integral part of the story; here, Tris finally starts to become Dauntless in a way that she hasn't before. Though she may not yet have the strength and fighting skill she will need to develop if she's going to make it through initiation, she has the intelligence and resourcefulness necessary for strategizing in dangerous or demanding situations, the likes of which Dauntless are often thrown into. The praise she receives from even the Dauntless-born initiates shows that she is truly beginning to fit in; she may have made the right choice after all.
And then, of course, her feelings for Four are beginning to blossom. Up on top of the ferris wheel, away from the stress and pressure of initiation where he is her leader, she finally begins to realize that being around him makes her feel like she's going to "burst into flames". This is the first time she really allows herself to notice her feelings. It's clear Tris and Four share a bond beyond instructor and initiate, but there may be some danger for both of them. Harboring feelings for her initiation leader may be a distraction, and Four is clearly struggling against Dauntless leadership. At this point, she can't afford to have anything get in her way, but Tris is also a young woman. This plot ushers in another coming-of-age for Tris - her "initiation" into romantic relationships.