This occurs in Chicago in the future, 16 year old's are choosing their new factions. Beatrice and Caleb Prior are a part of Abnegation and are yet to choose.
Beatrice learns that she is divergent and she struggles with this throughout the story.
Beatrice decides to join dauntless and Caleb joins Euridite. She changes her name to Tris and goes through the dauntless initation. Soon after, newspaper articles release about abnegation being corrupt.
Tris completes dauntless initiation and is injected with a serum that makes dauntless attack abnegation. Tris and Tobias are not affected because they are divergent. After attempting to save her family, they are captured.
Her mom saves her but dies doing it. Tris is reunited with Caleb her Dad. The three of them and Marcus break into the Dauntless compound and save Tobias.
Natalie and Andrew Prior
Tris and her allies leave the dauntless compound and flee by train to amity. This is only the beginning!