There are five factions in Beatrice's world that carry out the activities of everyday life. They are Dauntless, who is in charge of security both inside and outside the city walls, and Abnegation, which is in charge of the government.
When the story begins, Beatrice is a member of the Abnegation faction who is sixteen years old. She was raised to be completely selfless, but she doesn't think she fits the faction's ideals. Every teen over the age of sixteen takes an aptitude test to determine which faction they should join.
Beatrice is cautioned by the woman that revealing her identity would put her life in jeopardy. Beatrice goes home and begins considering her options based solely on that information. Caleb decides to join the Erudites at the Choosing Day ceremony, and Beatrice initially believes she will have to stay in Abnegation because she despises having to leave her parents alone. She does, however, make the decision to depart and join the Dauntless.
Beatrice is able to get through the initiation process without getting hurt, but she finds out that the Erudite had planned to use the Dauntless to overthrow the Abnegation. Through a simulation device, the Erudites take control of the Dauntless, and the Dauntless faction wage a bloody war against the Abnegation.