Beatrice chooses Dauntless and changes her name to Tris when she gets to the Dauntless compound. Throughout the story she struggles with her divergence.
Tris goes though Dauntless initiation with her friends Christina, Will, and Al
Peter, another initiate, reads about the article Erudite released about Abnegation being corrupt
After Tris completes initiation they were injected with a controlling serum. The next day all the Dauntless were sleepwalkers and were being controlled by the Erudite, and they were forced to kill the Abnegation. Tris was captured but then her mom saved her but died in the process and on accident Tris killed Will.
Tris was reunited with her dad and brother Caleb, and also Tobias's father Marcus. Together they went to the Dauntless compound to shut down the Erudite's Program and to save Tobias. But Tris's dad died saving her.
So then Tris, Tobias, Caleb, Marcus, and Peter go to the Amity Sector