On a summer's day in Rome, Roberto Mariani (Jean-Louis Trintignant), a withdrawn young scholar, encounters Bruno Cortona (Vittorio Gassman), a middle-aged man driving a stylish convertible. The chance meeting leads to drinks and eventually to an extended road trip out of the city. As the unlikely pair spend time together, they find out more about each other and even visit respective family members -- notably Bruno's beautiful daughter, Lilly (Catherine Spaak) -- on their impulsive outing.