Juan Oro would never know who his parents were or where he had come from. He had been raised by Yaqui Indians, and as a youth he was captured in a battle by the men of Don José Fontana, a wealthy Spanish grandee in northern Mexico. The don is advised to apprentice him to the notorious outlaw, Matiás Bordi, who had a long-standing truce with Fontana. Who better to turn Juan Oro into a true master of weapons and battle?
But Don José, whom Juan has come to admire greatly, asks one promise from the boy before he is released to Bordi: once his tutelage has finished, he will slay his mentor, the outlaw leader. Juan Oro promises the don he will do this . . . until the time comes, and he finds that it is not so simple.