To get the money to pay for a doctor for his father, Romeo bravely sells himself as a chimney sweep. On the way to Milan he meets Alfredo, a mysterious boy on the run heading to the same fate. Upon being separated and sold to their new bosses, the two boys swear eternal friendship. Romeo has to learn the hardships of a chimney sweep's job. His boss' daughter, Angeletta, is a girl with a heart illness who is not allowed to leave her room. She asks Romeo to bring the blue sky to her. Alfredo unites the sweeps in a secret union, the "Black Brothers" to face together the "Wolf Pack" gang, who constantly attack them. With their help, Romeo succeeds in bringing Angeletta's dream to her. Soon the brotherhood faces more hardships than cruel bosses or street hooligans. Alfredo reveals his secret: he has sold himself in the name of his sister Bianca. It is now up to the "Black Brothers" to stand up for the truth, to save Bianca and to protect their leader's life with their own.