The novel opens as Theodore “Theo” Boone finishes breakfast. He is 13 years old, and he eats with his dog Judge. After finishing his meal, he promises his mother, who is a divorce attorney, that he will stop by her law office after school. Riding his bike to class, he stops at the courthouse to see his friend April Finnemore. Her parents are divorcing, and she is indecisive about how to answer the judge when he asks her which parent she wants to live with. Theo advises her to choose her mother because the judge is more likely to agree with her.

Theo then stops to see Judge Henry Gantry, who is presiding over a big case the next day. Theo wants his class to be able to watch the trial on their field trip, and he asks the judge for 17 seats. The judge agrees.

Theo rides to school, where classes are “gender-separated” as part of a new policy. He tells his government teacher, Mr. Mount, that he procured seats at the trial the next day. He also goes to Spanish, which is taught by Madame Monique, a woman from Cameroon who speaks more than three languages.