In January 1952, Ernesto Guevara is a medical student in Buenos Aires, Argentina. His friend and fellow medical student, Alberto Granado, suggests that the two of them take a motorcycle trip through South America together, with the ultimate aim of seeing the San Pablo Leper Colony in Peru, in which Alberto is professionally interested. The men repair Alberto’s old motorcycle, which they affectionately and mockingly name “La Poderosa” (“The Powerful”), say goodbye to their families, and set off from Buenos Aires.
The men travel for some days and stop in Miramar, Argentina, to visit Ernesto’s girlfriend, Chichina, and her family. Although he and Alberto are setting out on a youthful adventure, Ernesto finds it hard to tear himself away from the comfort and excitement of his romance. He stays for eight days and gives Chichina a dog named “Comeback,” showing his intention to return to her side (although he never does).
After leaving Chichina and her family, the men cross into Chile, although they have to stop almost every few days because of La Poderosa’s many mechanical failings and accidents. Their frequent stops in rural towns lead them to meet people from all walks of life, from the mechanics who fix the motorcycle to local doctors who take an interest in them and feed and shelter them. They even tell local newspapers that they are leprosy experts (although they’re really medical students); consequently, local communities respect and help them, making for an easy journey.
In the north of Chile, they visit the Chuquicamata copper mine, a huge source of wealth for Chile (although not for its working class), which is run by U.S. mining companies. Guevara notes how dangerous the work is and asks his guide how many people died since the mine’s creation. This experience leads Ernesto to observe the rampant injustice that miners face and the devastation that capitalist industry controlled by foreign companies can inflict on local communities. While camping, Ernesto meets a mining couple who are homeless, having been blacklisted from the mines for their Communist beliefs (which were illegal at the time). Ernesto feels deeply sympathetic to the couple, and he comes to believe that Communism isn’t a dangerous ideology, but rather a natural response to class-based oppression and poor living conditions.
In Peru, La Poderosa finally breaks down for good. Because they now have to hitchhike or work for their passage between cities, the two men spend more time with the working class, especially indigenous farmers and laborers. Ernesto observes that the “Indians” face additional oppression because of their race, even from Europeans who are barely better off economically. Observing the traditional rituals of indigenous peoples, Ernesto is impressed with the strength and resilience of pre-Columbian cultures in the face of centuries of oppression.
Ernesto visits Cuzco and Lima, two cities that are important centers of European power and culture but that also contain the remains of the Inca civilizations that were there before. Ernesto visits ruins of fortresses and castles and is deeply moved by their power and sophistication. By examining these cities’ layers of ancient, colonial, and modern architecture and infrastructure, he demonstrates the European attempt to suppress indigenous culture by erasing evidence that it existed. Ernesto finds it inspiring that indigenous cultural sites and practices have survived these repeated attempts at obliteration, and he views this survival as evidence that the indigenous proletariat can and will rise up to reclaim the political and economic power that is rightfully theirs.
In Lima, Ernesto meets Hugo Pesce, a doctor in charge of the national leprosy program. Pesce helps direct Ernesto’s exploration of the city and he eventually sends Ernesto and Alberto to the San Pablo Leper Colony deep in the Amazon. Ernesto observes the appalling living conditions at the colony, but he is inspired by the work of the doctors and the hopeful attitudes of the patients. Although he is studying to be a doctor and he came to observe the treatment of leprosy as a disease, he writes about the lepers in terms of their political oppression, showing that his thoughts are shifting away from medicine and towards political activism.
After this, the young men travel north to Colombia. In Bogota, they observe conditions under a particularly repressive right-wing regime. Ernesto says that the constant presence of police in civilian life erodes personal dignity, and he predicts (correctly) that these conditions will help foment revolution.
In Caracas, Venezuela, Ernesto and Alberto finally separate. Although the trip has changed and inspired both of them, it changes them differently: Alberto begins to seriously consider a career as a leprologist, while Ernesto abandons the medical profession and begins to develop a Communist ideology.
After Alberto leaves, Ernesto travels by himself through rural villages in Venezuela. Here, he meets an enigmatic European stranger who has fled his own country because of his revolutionary actions (although Ernesto doesn’t specify what these are) and now travels around South America, waiting for the chance to participate in another movement. The stranger tells Ernesto that when revolution comes, it will be huge and “impersonal,” and that the creation of a new, proletarian society will require the sacrifice of many lives.
This prediction inspires Ernesto. At this point, he becomes completely committed not only to Communist ideology, but also to revolution by violence. He says that humankind is divided into “two antagonistic halves,” the oppressor and the oppressed, and he affirms that when it comes time for these groups to battle, “I will be with the people.” Ernesto envisions himself “consumed with fury,” fighting and killing on behalf of the proletariat. Ernesto’s final paragraphs offer the prospect of a society with more justice and equality, but he warns that this new world must be purchased through violence and sacrifice.