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.

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.

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.

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 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.

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.

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.

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.

Alfredo wants to restore his honor before the King of Italy and accuse his aunt and uncle of murdering his parents. Unfortunately, the Wolf Pack lure him into a trap and lock him in the sewers. Romeo and the Black Brothers await his arrival so they can sneak into the banquet, but Romeo, seeing that he does not arrive, decides to go in search of him.

The big moment is here! Alfredo and his uncle Maurizio stand before the king of Italy. Both have badges in their hands, but only one belongs to the Martinis. When the king asks which badge has the secret sign of blessing, only Alfredo knows the right answer. The evil uncle is finally exposed.

Spring has fallen and Romeo's contract with Maestro Rossi is over. It is time for Romeo to say goodbye to Milan and return home in Sonogno. Some of his friends have already left, while others still have to stay a while longer. Professor Casella offers to drive Romeo and the other boys halfway to their home towns along with Bianca. Before leaving, they visit Alfredo's grave one last time, where they meet the Wolf Pack.