Authors note (SPOILERS): it's a year after the rebellion. Tris is dead and Four is in a deep depression. This is the year Carly turns sixteen. At her Choosing Ceremony she catches someone in the Dauntless sector starring at her. From Amity she goes to Dauntless. There is one thing she knows. Don't follow in Tris Priors footsteps. (I have not finished reading Allegiant but I know what happens to Tris)