Cara is Will's sister from Erudite. She visits Will at the Dauntless compound during Visiting Day and is introduced to his fellow initiates Tris Prior and Christina and their visiting families. When Cara realizes that Tris and her mother were Abnegation, she insults their faction, claiming that Abnegation is full of lies. When Tris threatens to punch her face, Will defends her and Natalie Prior pulls Tris away, showing her Abnegation traits.
During Visiting Day, Cara comes to visit her brother, Will, and meets Tris and her mother at the Dauntless compound and is introduced to his fellow initiates Tris Prior and Christina and their visiting families. She finds out that Tris and Natalie are Abnegations, and insults their faction and Tris's mother by saying "Do you know what she is? She's a council member's wife is what she is. She runs the charity that supposedly helps the Factionless. You think I don't know that you're just hoarding goods to distribute to your own faction while we don't get fresh food for a month, huh?" And later, after Tris's mother tells her gently that she must be mistaken, Cara shoots back by saying "Mistaken. Ha. I'm sure you're exactly what you seem. A faction of happy-go-lucky-do-gooders without a selfish bone in their bodies. Right," After this, Tris threatens to break Cara's nose and is stopped by Will and her mother.
During the Dauntless and Erudite attack on the Candor compound, Cara was among the 'invading' Erudites, who defects and instead evacuates a group of loyal Dauntless to a fire escape that the Dauntless traitors had not sealed off, allowing them to rally the unsuspecting attackers. Tris avoids Cara and Christina because she is guilt-ridden after killing Will when he was in the stimulation. Cara was said to have left Erudite after she saw an Abnegation woman get killed while she was on a mission for Jeanine Matthews.
When Tris listens in on a conversation between Cara and Christina, she hears Cara trying to comfort Christina, who still hasn't gotten over the fact that her friend killed Will. She tries to make her see why Tris did it, explaining things from the Erudite's logical point of view, saying that what Tris did was out of panic, and not malice, since she was unable to reason with Will while under the simulation. Cara tries to explain that Tris reacted the Dauntless way, shoot and kill. She also pokes fun at Tris' judgement and hints that Tris has several character flaws. Christina is slightly offended, but she is too sad to be angry. To even lighten the mood, Cara joked about Tris' long nose and how Christina can avoid wanting to punch it, which makes Tris insecure about the length of her nose. Tris finds her hand automatically going to her nose to check. She is angry at Cara, but she gets over the anger shortly.
Tris later tells Cara to escape to Amity headquarters along with the others as they leave the Candor compound before the Dauntless-Erudite's arrival.
Cara is also among those in the Amity compound who join the infiltration of the Erudite headquarters.
Cara was imprisoned with Tris and Christina after Evelyn Johnson and the Factionless took control of the city. Cara was a leader of the Allegiant along with Johanna Reyes, and among those to leave the city. During the time she spends outside, she seems to become closer to the rest of the group, especially Tris and Tobias Eaton. As Tobias is gone when Tris dies, Cara is the one who tells him that Tris was killed. Cara, along with Caleb Prior works in the laboratories of the Department of Agriculture after the experiment is ended.
In We Can Be Mended she is engaged to Matthew.