Prosper and Bo. The entire story is centered around their escape from their Aunt Esther and Uncle Max. The brothers have a very close relationship and don't want to be separated. After their mother's death the Hartlieb's wanted to adopt Bo and send Prosper off to boarding school. Prosper tries his best to protect his young brother throughout the story and in the end it is Bo's bad behavior that gets them off the hook with Aunt Esther.
Victor Getz. He is a detective hired by the aunt and uncle to find the boys in Venice. Victor creates the suspense in the initial part of the story as he bumps into them twice and finally finds their hideout. After meeting with the two boys he starts to feel sorry for them and decides to help them by not telling their aunt and uncle where they are hiding.
Scipio. He is the self-proclaimed Thief Lord and is the one who provides for the gang of orphans until Victor exposes him. He pushes the story to the climax by agreeing to the job offered by the Conte and finally tricking Barbarossa into taking a ride on the magical merry-go-round.
Ernesto Barbarossa. He is key to the story because he is the one that offers the Conte's job to Scipio and his gang, leading them to the climax of the story. He is also a part of the climax when he breaks the magical merry-go-round and leaves Scipio an adult and himself a child. Finally, he decides to charm Aunt Esther into adopting him and she finally leaves the boys alone.