El Búfalo de la Noche - Gregorio is a 22 year-old schizophrenic with two great loves: his girlfriend, Tania, and his best friend, Manuel (played by Luna). While Gregorio checks in and out of a psychiatric hospital, Manuel and Tania begin an intense romance behind his back. Once released from the hospital, after an apparent recovery, Gregorio begins to reconcile with Manuel. Days later, however, Gregorio commits suicide, but not before setting up a chain of events that will lead Manuel on a complex and painful journey into the depths of madness and despair, and ultimately to the meaning of true love. When the novel was published in 1999, author Guillermo Arriaga gave it to Diego Luna with the objective that when it was adapted for film in the future, Diego would become the main character.