Romeo is an 11-year-old boy who lives humbly with his family in Sonogno, a small Swiss village near the border with Italy. The village is suffering a long drought, and Romeo's family has had the worst of it, as they are also under debt. Their last hope is the only corn field that has survived so many months without rain. Romeo wants to participate in the pole climbing competition, in which several boys compete to get a trophy placed on top of a pole. Meanwhile, Luini, a mysterious man known as the god of death, arrives in the village. He buys orphaned or poor children, which he later sells them as chimney sweeps in Milan, and now he has his eyes on Romeo.

The fire started by Luini devastates the only cornfield that Romeo's family has left. Romeo's family rush to the field to try to save the domestic animals, but Roberto injures his head while leaping out of the flames. After this tragic incident, Roberto's injury worsens and a rumor about Roberto intending to sell Romeo to the god of death spreads in the village. Then, after an argument with his father, Romeo runs away from home and hides in Anita's barn, where he hears that Roberto is not his real father. Meanwhile, Luini approaches Roberto and pressures him to sell his son.

Due to the injures suffered during the fire, Roberto's condition worsens to the point of going blind if he is not treated urgently. However, the family's financial situation prevents them from paying for the services of Baresi, the only doctor in the area. Romeo, aware of the situation, secretly signs a contract with Luini to go to work in Milan as a chimney sweep in exchange for the latter bringing the doctor to treat his father. The contract will be for six months, so Luini would be back to the village in spring. However, Anita hears that no children sold in Milan have returned.

After being treated by doctor Baresi, Roberto will recover and will not go blind. Romeo has sacrificed himself for the sake of his family and must now leave the village. On his way to Milan, Luini tells Romeo to go to the town of Locarno and wait for him there. Along the way, Romeo is mistaken for an apple thief, but is saved by Alfredo, a boy who is also heading to Milan to become a chimney sweep as Romeo. In Locarno, Alfredo's bag falls into a river after being stolen, so Romeo throws himself into the river to recover it.

Luini locks up the boys before crossing the lake by boat to get to Milan. Among them is Dante, the boy who had stolen Alfredo's bag, who tells them that his brother also went to work in Milan, but ended up dying of starvation. The night before leaving, Dante devises a plan to escape.

The boat in which Romeo and the others are travelling to Milan is hit by a storm and sinks. Miraculously, Alfredo and Romeo manage to save themselves. Luini is also saved from drowning by Romeo. On the shore, Alfredo tells Romeo about his tragic past and how he was separated from his sister Bianca. The next morning, they leave for Milan.

In Milan, Romeo and Alfredo are sold as chimney sweeps to different bosses, having to separate, but not before swearing eternal friendship. Romeo is taken by Rossi, his buyer, to his house, where he will start a new life.

Cleaning chimneys is harder than Romeo could imagine. And worst of all is that when he comes home tired from work he doesn't get a piece of bread. Rossi's family seems to hate him. However, an angel who lives in the house cares for him.

Romeo goes to clean Professor Casella's fireplace who, to thank him, gives him an illustrated book. However, Romeo cannot read, so the teacher offers to teach him to write his name. Upon his return home, he finds a letter left by the girl who lives in the same house, Angeletta. But, how will Romeo know interpret what is written on it?

Romeo manages to get the key which keeps his door locked, so he can go out to meet Angeletta, becoming friends. She tells him that, due to her illness, she has not been able to leave her room for many years, which prevents her from being able to behold the vast blue sky. Then Romeo makes her a promise, but the Wolf Pack gang will get in her way.

Romeo watches from the rooftop of a house that one of the Wolf Pack members is ambushed by another gang of boys, but then the rest of the pack appears and a fight breaks out, wich is won by the Pack boys. Anselmo, who was not present during the fight, is seen by Romeo while he devises a plan to gain recognition from the rest of the pack members.

Romeo finds Anselmo lying on the street and covered in bruises. Anselmo tells Romeo that he confronted Tachioni because he hates outsiders and wants to kick Romeo out of town. Romeo, full of rage, runs in search of Tachioni.

Romeo fights the Wolf Pack, who think he has denounced them to the police, but is saved at the last minute by a masked boy. Chased by the police, Romeo tries to sneak into a carriage going to Venice to escape Milan.

The carriage Romeo has sneaked into contains explosives that the robbers intend to use to blow up the police station and free their imprisoned friend.

After proving his innocence, Romeo's conditions at Rossis' house get better. Marcello gives him a day off and Romeo decides to search for Alfredo in the streets of Milan. During his search, he meets other young chimney sweeps.

After a long time, Romeo and Alfredo finally reunited and joined other young chimney sweeps to form the Black Brothers fraternity with Alfredo in command to confront the Wolf Pack. Romeo tries harder to learn to read inspired by Alfredo. Knowing that Alfredo only has one book and that it is in poor condition, Romeo introduces him to Professor Casella, who offers him to choose a book. Alfredo borrows one from Voltaire dealing with freedom and equality.

Since the Wolf Pack has no intention of stopping picking on the chimney sweeps, the Black Brothers, fed up with running away, decide to stand up to them. Thus, they draw up a plan to fight them in San Babila church. Meanwhile, Giovanni, the leader of the Wolf Pack, goes alone to a meeting with the rival gang Scorpion.

As retaliation for losing the fight at San Babila church, Michaelo was kidnapped by the Wolf Pack. To release him, their leader Giovanni demands that the Black Brothers hand over Alfredo to them. Alfredo decides to show up alone, but Romeo doesn't want to leave him alone and offers to go with him. A new battle between the two gangs is approaching.

Marcello Rossi receives a letter from his mother, Mimi, announcing she will pay them a visit soon. Rossi has not seen her mother in a long time, and his memories of her are not very pleasant, so in the beginning he does not like her visiting. On the contrary, Edda and Anselmo, who initially were not very pleased about her coming, are excited after learning that Mimi is bringing a treasure for Anselmo.

Romeo and Angeletta meet the old puppeteer Teo and little Nana. Teo has a sad secret: Leon, his son, left him and his granddaughter after a quarrel. He would rather be a doctor than a puppeteer. Now Teo wishes nothing more than to see his son again. Angeletta asks Romeo and the Black Brothers to find Leon. Also, Matteo is about to reveal a secret about Angeletta to Romeo while talking with Rossi.

Matteo tells the boys the story of Marcello Rossi and Angeletta: a countess named Isabella is the girl's grandmother. Romeo now wants to find out everything and secretly follows Rossi to a castle where the Ice Queen, as Isabella is called by the others, lives.

Angeletta's greatest wish is to meet her grandmother, the Countess Isabella Montovani, before her serious illness progresses. The Black Brothers therefore drive Angeletta to the castle in a wooden cart. Rejected by the security guard, they climb over the wall. They are discovered and there is a chase in the castle courtyard.

Angeletta's condition is deteriorating rapidly. The so-called Ice Queen Montovani wants nothing to do with her granddaughter. Even asking chimney sweep Rossi is useless. The Black Brothers therefore clog the chimneys of Montovani Castle. They want to force the Countess to stay in touch with Angeletta.

In Milan, a wedding of the nobility is taking place and all rich and noble people of the area are invited. Even the king of Italy is expected to come. Then Romeo accidentally meets Bianca, Alfredo's sister who was believed to be missing. When he conveys the good news to him, he learns Alfredo's mysterious story.

Alfredo and Bianca are still on the run from their relatives. Their aunt and uncle want the badge that Alfredo hid. This badge was bestowed on Alfredo's father by Carlo Alberto, the father of the current Italian king, and legitimizes the Martini's fortune.