The book is set in the Republic of America, a police state located in the Western United States who has waged war against its eastern neighbor, the Colonies of America, since its creation in 2054. The country is led by the Elector Primo, who has rigged elections to rule for several decades, with the capital at Denver. Other than a huge gap between the rich and the poor, the country also mandates its citizens to partake in a Trial once they turn 10 years old to deem their fitness for the army; if they fail, the public is told they are sent to work in labor camps.
In Los Angeles, Daniel “Day” Altan Wing, a rebellious 15-year-old deemed as the most-wanted criminal in the country for having escaped the labor camps and done subversive actions, stages a failed attempt to steal a medicine from the Central Hospital for his younger brother, Eden Baatar, who is infected by a plague (released by the government to create biological weapons) that has caused their neighborhood’s quarantine. However, he ends up becoming accused of the death of Captain Metias Iparis. Metias’ younger sister, June “Junebug”, a 15-year-old prodigy and the only person to score perfectly in the Trial, seeks to find Day in revenge. Posing as a street urchin, she is saved from a wild Skiz fight by Day and his friend, Tess. Initially unaware, she falls in love with him, but when she discovers his identity, she informs the army to capture him and his family; when he rebels, Thomas Bryant, a friend of Metias and June, is ordered by Commander Jameson to murder his mother, Grace.