To Prosper, staying with his true family, his brother, is the most important thing in the world. Prosper and Bo have family who do not appreciate or love them. Aunt Esther and Uncle Max Hartlieb do not want Bo because they love him, but rather because he is little and cute. Scipio as well has a family who does not appreciate him. It appears that his mother is no longer living, and his father is constantly disappointed in him. Dottore Massimo wants Scipio to be like a pet, obedient and small, acting like a puppet, with Dottore Massimo pulling the strings. Together, the children find that family does not necessarily mean the people who gave birth to you, but rather, family means the people that support you and care for you. Family is really about love. The children become a family as they work and live together, and Victor and Ida become like parents to many of the children.

Friendship is another theme that is prevalent in the novel. The children readily accept each other as friends because they are united by a common front: survival. Even though Scipio is not really an orphan, he leads the others to believe he is, so they embrace him as a friend. When the truth comes out and he is revealed as the son of the wealthy Dottore Massimo, the friendship is destroyed for a while, because he has lied to the others. Prosper, however, is the only one that can see through Scipio’s bravado and realizes that he is in some ways just as much an orphan as the rest of the children are, because he lives without love from his father, and lives in fear of Dottore Massimo. Scipio must gain back that friendship by proving himself to the others. Victor and Ida, however, must work at gaining the friendship of the children, because they are adults and a possible threat to the children. Victor has the power to turn the boys over to the Hartliebs, but once he realizes the boys’ worth and spends time with them, the children and Victor become good friends. Victor makes the promise not to tell the Hartliebs about the boys, and his help in this matter makes the children realize that Victor is a friend and is no longer a threat. Ida begins as a mark—she is just the woman who has the wing the children need to steal. However, when she catches them, instead of just calling the police, she listens to the children and analyzes their story, creating a situation where everyone can get what they want.

Disguises and identity is another prevalent theme throughout this work. Several characters rely on disguises in order to hide who they truly are. Victor wears various false beards, mustaches, and glasses in order to do his detective work. He relies on disguises to hide his identity. The children discover that Barbarossa (the redbeard) is also a phony: he actually dyes his beard to look more intimidating and special. Scipio hides his true identity of the son of the Dottore by creating the persona of the Thief Lord. He wears high heels in order to appear bigger, and a mask to look mysterious and hide his face from people who may recognize him. Scipio rejects his life as a wealthy son, and creates a whole story in order to be someone else so that he could have control over one aspect of his life. Prosper and Bo even hide their identities when Aunt Esther and Uncle Max are searching for them, by cutting Prosper’s...