A young peasant, Aldo Contini, come to Rome in search of a job. In order to observe two women who are sunbathing on a terrace, he climbs up to a roof, not knowing that he is on the roof of a palace, in which has been killed a little girl. Forced to escape, on his own from the moment in which someone discovers the corpse, he is mistaken for the assassin and only the providential participation of a policeman succeeds in saving him from the furious vengeance of an angry mob. In possession of some clues, he is subjected to a brutal interrogation by the police, during which Aldo, after having uselessly protested his innocence of the crime, ends up confessing to the crime in front of the enquirers.
El Extranjero en esta ocasión topará con la famosa banda conocida como “El tesoro de la frontera”, llamada así al haberse puesto precio a la totalidad de sus miembros por 10.000 dólares, que se ha apoderado, tras matar a todos sus ocupantes, de una diligencia cubierta de oro; por lo que decidirá enfrentarse a la banda con el objeto de cobrar la recompensa que ofrecen por ellos, además de apropiarse de la diligencia, para lo que contará con la ayuda de un peculiar predicador.
