PARK CITY, Utah — Author and screenwriter Guillermo Arriaga says his novel about sexuality among a dysfunctional group of young friends, “El Bufalo De La Noche (The Night Buffalo),” is more easily understood and accepted by younger people, a trend he expects will continue for its film adaptation.“Wherever it’s published, young people say, ‘Man you really got it,”’ Arriaga said. “And old people it’s like, ‘Why should I care about these characters?”’

The film, which premiered last Friday at the Sundance Film Festival, stars Diego Luna, of “Y Tu Mama Tambien,” and is the first full-length feature for director Jorge Hernandez Aldana.

“I wanted to do a movie that is kind of a roller coaster of emotion. People are shocked after the movie,” he said. “This is the kind of movie that invites you to watch it again and again.”

Luna’s character, Manuel, has a best friend who is schizophrenic and has spent time in a mental hospital. While his friend, Gregorio, played by first time actor Gabriel Gonzalez, is in the hospital Manuel has started dating Gregorio’s girlfriend, Tania, played by Liz Gallardo. Gregorio is released from the hospital and he and Manuel seem to be mending their friendship. But then Gregorio kills himself and leaves a box of notes for Manuel that contain messages for those he has left behind.

Already overcome by feelings of grief and betrayal, the box sends Manuel into the abyss of his friend’s madness.

The themes of love, betrayal and death are common in Arriaga’s work, which include the screenplays “Amores Perros,” “21 Grams,” and “Babel” — for which he received a 2007 Golden Globe nomination. His screenplay “The Three Burials of Melquiades Estrada,” won the best screenplay award at the 2005 Cannes Film Festival.

In “The Night Buffalo,” Arriaga examines how his common themes are navigated by a young person ill equipped for the task. He said the sense of confusion and disconnection that is at the heart of Manuel’s struggle is one people under the age of 33 are more apt to relate to.