The Treasure of the Sierra Madre by B. Traven
Three down-and-out Americans meet by chance in the Mexican city of Tampico and discuss how to overcome their financial distress. They then set out to discover gold in the remote Sierra Madre mountains. Once in the desert, Howard, an experienced old-timer, quickly proves to be the toughest and most knowledgeable; he is the one to discover the gold they are seeking. A mine is dug, and much gold is extracted, but one of the men (Dobbs) soon becomes greedy and begins to lose both his trust and his mind, lusting to possess the entire treasure. One day, another prospector named Lacaud follows one of the men (Curtin) from a nearby village back to the men's camp. Although the men do not initially trust Lacaud, they decide to allow him to stay and camp with them.