Marco Rossi, a nine-year-old Italian boy in late 19th-century Genoa, endures familial fracture amid crushing poverty. His father, Pietro, directs a debt-ridden charity hospital, while his mother, Anna, departs for Argentina as a domestic servant, leaving Marco embittered toward Pietro and excluded from family choices. When his older brother Tonio departs to train as a locomotive engineer, Marco’s isolation hardens into resolve: he will reunite with Anna.

Her letters stop. Secretly laboring at a wine shop, Marco saves coins for passage to Argentina, then stows away on a Brazil-bound ship with his brother’s pet monkey, Amedeo. Aboard, he scrubs kitchen pots, dodges detection, and befriends crewmen Rocky and Leonardo, who aid his onward journey to Buenos Aires.

Argentina tests him with thieves, labyrinthine bureaucracies, and hunger. A puppeteer, Peppino, and his daughter Fiolina—a girl mirroring Marco’s loneliness—offer temporary solace. His compassion overrules his mission when he spends his train fare to save a dying child, stranding him. Robbed, ejected from trains, and reduced to begging, he persists, aided by a Roma family’s gift of a donkey.

The quest reveals betrayal: Anna’s brother Francesco stole her letters and earnings. Marco, undeterred, treks to Tucumán, finding Anna frail and feverish. Their reunion reignites her fight to survive surgery, enabling her eventual recovery and return with him to Italy.

Marco sheds childhood resentment through hardship, emerging resilient and empathetic. He connects with marginalized communities, inspires Fiolina’s hope, and reconciles with Pietro, who now recognizes his son’s maturity. His odyssey—forged by stolen letters, a monkey’s chatter, and a donkey’s plodding steps—cements perseverance and familial bonds as antidotes to despair.