In the book Hoot, how does the main character contribute to the development of the theme?

Roy Eberhardt is the main character in Hoot. A strong theme in the book is that one should get involved and stand against injustice. Roy contributes to the development of this theme in three important ways.
As the book starts out, when Roy is on the school bus, he sees a barefoot boy running across lawns as the other children are going to school. He is intrigued by the mysterious boy and goes in search of him. When he finds the strange boy living by himself in the woods, he wants to find out more and gives him a pair of his own shoes. He keeps pursuing the mystery boy, despite threats from Beatrice Leep. He stands in sharp contrast to Beatrice's father, who is so uninvolved in his step-son's life that he doesn't even know he has run away from school. Roy is willing to get involved where others aren't. 
Roy also supports the theme of getting involved and standing against injustice when he defies Dana Matherson, the bully. Dana terrorizes new and younger kids on the bus and at school with impunity. No one stood up to him before Roy. He almost chokes Roy, but Roy fights back, breaking Dana's nose. When the school fails to discipline Dana for fear of a lawsuit, Roy takes matters into his own hands and lures Dana into committing a crime, for which Dana is arrested and sent to juvenile detention. When Dana gets locked up, Roy "felt guilty about making up the bogus cigarette story, [but he] also couldn't help but think that putting Dana behind bars was a public service." Again, Roy gets involved where others have let the matter slide, and justice is achieved in the end.
Finally, Roy's attempt to save the owls is an example of how an everyday citizen, even a minor, can get involved in community issues and stand against injustice. Mullet Fingers tries to protect the owls, and instead of brushing the boy off as crazy Roy investigates and learns the owls are protected by law. Roy then attempts to find out whether Mother Paula's has followed the law, and he even goes to city hall to try to look at the company's file. He raises the issue in his history class, which inspires many of his classmates to come out to rally against the groundbreaking. Because of his efforts, the story garners local and then national media attention, and the pancake house company's illegal actions are exposed. By getting involved and taking a stand against injustice, Roy creates positive change in his community and beyond.
Roy demonstrates that ordinary citizens, even teens, can impact society positively when they get involved and take a stand against injustice.