Central Italy in the winter of 1944. The war leaves a trail of death and desperation, pillaging and hastily abandoned towns.
In this confused and dramatic scenario, a peculiar group of animals wanders around the devastated countryside: Boldsteed, a middle-aged Sicilian horse with a strong build and a generous heart; an American military dog called Jack and his inseparable bee-pilot called Bee-17; Aurelia, the cat from Rome with an amazing talent for getting out of the stickiest situations; and lastly Christopher, the long-winded rooster from Tuscany.
Our group's vagabond life is disrupted by their encounter with a small boy who looks about five years old. With his bewildered expression, he emerges from the rubble having miraculously survived an air raid. Because of the shock he can no longer speak, and his vocabulary is blocked on repeating the same two words: "Boom! Boom!"... so this is the name the animals give him.
The band of five decides to team up, take Boom Boom under their care and protection, and reunite him with his family.