Road movies provide screenwriters with a built-in structure. It allows them, in the immortal words of the Queen of Hearts, to “begin at the beginning, go on until you reach the end, and then stop!” But what happens when an ending isn’t really the end? Or when the “real” end sends us down a different road altogether?

The Motorcycle Diaries, directed by Brazilian Walter Salles (Central Station), re-creates an actual 1952 journey through South America made by two Argentineans—Alberto Granado (Rodrigo de la Serna), a 29-year-old biochemist, and Ernesto Guevara (Mexican star Gael Garcia Bernal), a 23-year-old medical student. The reason we care about this road trip 50 years later is that Ernesto became the revolutionary “Che” Guevara, who remains a poster boy for guerrilla movements worldwide. (When I was in college the famous Alberto Korda photo of Che was as popular in dorm rooms as posters of Steve McQueen and Jean-Paul Belmondo.)

The film, scripted by Puerto Rican playwright José Rivera, is based on a pair of books written by the young adventurers about their five-month, 5,000-mile journey. Alberto’s book, Traveling with Che Guevara, is the more factual. Ernesto’s The Motorcycle Diaries: Notes on a Latin American Journey was pieced together from notes that were found after his death.

The journey takes the pair from Buenos Aires, where Ernesto’s rich and attractive girlfriend lives, through Argentina and into Chile, Peru, Colombia and Venezuela. The two, who are polar opposites in temperament—Alberto is outgoing and robust, Ernesto shy and asthmatic—meet miners and thugs, bar maids and hookers, doctors and lawyers, lonely wives and jealous husbands. Their eyes are opened to the poor, the corrupt and the uneducated, as well as to the magnificent beauty of the landscape (a landscape made even more stirring by the stunning photography of French cinematographer Eric Gautier and the seductive guitar music of Gustavo Santaolalla).

Salles employs these buddy-on-the-road misadventures to set up the sections in which Ernesto begins to develop his political awareness. The consciousness-raising reaches its zenith when the pair arrives at a leper colony on the Amazon River in Peru. Ernesto immediately bonds with the lepers themselves (one could not ask for more Christlike imagery), boldly ignoring the entreaties of the timid doctors and the insensitive nuns, who refuse to feed the patients unless they attend Sunday mass.

The leper colony transformation culminates in a highly symbolic act: Ernesto swims across the dangerous Amazon on his birthday, in the dead of night, to reach out to the lepers on the other side. (This is a bit of movie mythmaking; the real swim as documented in Alberto’s book isn’t nearly as dramatic.)

If all you know about Che Guevara is what you glean from this film and absorb from popular slogans, you might think he went on to a lifetime of altruistic, nonviolent service. He didn’t. He participated in a series of bloody rebellions, from Guatemala to Cuba to the Congo, before being killed trying to overthrow the government in Bolivia.

The brutal reality of Che’s later life and death makes this look back at his youth sentimental and thin. A famous North American road film, Easy Rider (1969), was at least willing to have the main character sum up his journey by saying, “We blew it.” But Salles and Rivera seem afraid of presenting the moral puzzle that was Che, and terrified of getting dust on his sainted memory. Exploring the shadows of his life would have made for stronger cinema.