There are 2 main characters--June and Day. They are from different social classes but both of them are looking to survive amidst war and grief in their personal lives. June is the prodigy who made a perfect score on her qualifying test while Day supposedly failed his. June has been sent to the best school and even after she has a personal tragedy is expected to find the Republic's worst criminal. Day is a renegade because he failed his test and bad things happen to the ten year olds who do not pass the test. You guessed it--Day is the renegade that June must find and bring to justice. She does indeed bring him to justice, but it is not exactly what she envisioned.
The book has many nuances that I appreciated including allusions to present United States as well as the weaving of the different characters' stories.