Verona, 1970. Sergio is a nine-year-old only child. Though apparently well adjusted, he is nicknamed "the Lone Ranger" thanks to his solitary habits. His middle-class parents Anna and Paolo are going through a rough patch and unhappily debate whether to terminate Anna's unwanted pregnancy. During a long summer vacation in the country, the imaginative Sergio at first fiercely resists the prospect of a new sibling; then battles with an awful sense of guilt when his imaginary brother fails to materialize. This impish figment of his hyperactive imagination refuses to go away, however, and comically becomes an inseparable if annoying companion.