Four down-on-their-luck European men, including Mario Livi (Yves Montand), are hired by an American oil company to drive trucks loaded with nitroglycerin over treacherous mountain dirt roads in South America. Friendships are tested and rivalries develop as they embark upon the perilous journey, which includes navigating rough roads, construction barricades, and physical obstacles, all while dealing with their own personal demons, including Mario's flirtatious nature, Jo's increasing cowardice, and Luigi's terminal illness. The journey culminates in a dramatic explosion that kills Luigi and Bimba, forcing Jo to confront his mortality, and ultimately leading to Mario's triumphant return home, albeit at a high cost to his own life.