During the Ferragosto holiday, Bruno Cortona [Vittorio Gassman]—a thirty-six-year-old man riding in a flashy, expensive Lancia Aurelia—tears through the streets of Rome. He persuades timid law student Roberto Mariani [Jean-Louis Trintignant] to let him use his phone, and when Bruno is late for a meet-up with friends, the two set off on a long road trip along the Via Aurelia, winding through Lazio and into Tuscany. What begins as a simple favor soon reveals the core contrast between them: Roberto is cautious and proper, while Bruno is exuberant, coarse, charismatic, devil-may-care, impulsive, and unabashedly immature. Bruno drives with a reckless energy, constantly trying il sorpasso—honking, tailgating, and weaving past cars in front of him—and Roberto, despite their differences, finds himself drawn to this reckless charisma.
As they stop to visit Roberto's relatives, Bruno points out the aunt's cuckolded marriage and notes that one relative seems nostalgically fascist, exposing the undercurrents of a family history Roberto hadn’t fully confronted. The journey quickly uncovers Bruno's real situation: a man who is socially skilled but morally adrift, financially strapped, and masking his insecurities behind bravado. The two men drift closer in odd companionship, with Bruno urging Roberto to smoke, party, drink, and pursue the woman he secretly admires.
That evening, Bruno impulsively visits his estranged wife Gianna Cortona [Luciana Angiolillo] and their daughter Lilli Cortona [Catherine Spaak]. Through this tense reunion, Roberto learns crucial backstory: Bruno and Gianna married in their early twenties; Bruno has not been involved in Lilli's life; an annulment remains unresolved; and Bruno once stole 600,000 lire that Gianna had set aside to bribe a monsignor for the annulment. Gianna makes it clear that one day is enough to understand Bruno’s lack of hidden depth. Bruno is stunned to discover that Lilli is about to marry Bibi [Danilo Borelli]—a older, more conventional man who has his own stability—while he hypocritically complains that Lilli has started smoking. He attempts to seduce Gianna again, but she dismisses him firmly, and with nowhere to stay, Bruno and Roberto end up sleeping on the beach.
The next day, Gianna, Lilli, and Bibi join the beach cruise, and Bruno circles a young woman who is, in fact, Lilli in disguise. Yet Lilli does not humiliate him; Gianna invites the entire group onto the boat, and Bruno misreads this as a chance to win Lilli back. He presses his luck, while Roberto, more at ease among the women, enjoys the smiles and compliments he receives, though his own crush remains unacted upon. He sees in Bruno a charisma he admires even as he is wary of its consequences, and, over time, Roberto resolves to imitate Bruce’s swagger more than his scruples.
In a tense exchange, Bibi explains that he does not expect Lilli to love him but will care for her anyway. Bruno’s vanity meets reality when he bets 50,000 lire on a ping-pong match and wins, but Bibi, feeling insulted, leaves with Gianna and Lilli. The victory is a hollow triumph that reveals Bruno’s mask as nothing more than performance. Returning home, Roberto finds himself adopting Bruno’s loud, confrontational demeanor on the road, shouting at other drivers and pushing Bruno toward ever riskier driving.
The journey’s crescendo comes on a cliffside road, where another driver’s fury erupts into a dangerous standoff. To avoid a collision with an oncoming truck, Bruno veers off the road and plummets off the cliff, killing Roberto. When the police arrive, they question Bruno about his companion, but he realizes—too late—that Roberto had told Gianna his last name, and now the name slips from Bruno’s memory as the life he shared with his friend fades into memory. The tragedy exposes the thin line between bravado and consequence, leaving Bruno to confront the cost of a life lived in the speed of a thrill ride.
