Ten-year-old orphan boy Sebastian lives with his faithful mountain dog Belle in a secluded alpine village with his grandfather, César. He receives word that his aunt Angelina's plane has crashed and he decides to search for her.

September, 1945. Sebastian impatiently waits for the return of his friend Angelina, whom he has not seen for two years. When the plane carrying the young woman to her small village in the Alps is reported to have crashed in the mountains, Sebastian is convinced that Angelina is still alive. Along with his faithful dog Belle, Sebastian embarks on the most dangerous adventure of his life . . .