Leon Alastray, played by Anthony Quinn, is a former soldier who has become an outlaw in Mexico. He seeks sanctuary at a church in a small village called San Sebastian, where he meets Father John, played by Sam Jaffe. The two men strike up an unlikely friendship, and Alastray agrees to escort Father John to another church in a neighboring village.
When they arrive in San Sebastian, the village is deserted except for a few cowardly residents who are hiding in the hills. The villagers explain to Alastray that they are regularly attacked by Indians, who steal all their supplies and leave them with nothing. Father John tries to rally the villagers and convince them to fight back, but they are too afraid.
One day, Father John is murdered by one of the Indians, and the villagers mistake Alastray for the priest. They believe that he has been sent by God to save them from their plight. Alastray initially tries to tell them the truth, but they refuse to believe him.
A miracle seems to occur when Alastray blesses some water, and it heals a sick child. This convinces the villagers that he is truly a priest, and they accept him as their leader. Alastray begins to embrace his new role and helps the villagers regain their confidence and defend themselves against the Indians.
Along the way, Alastray falls in love with a local woman named Kinita, played by Anjanette Comer. However, their relationship is complicated by the fact that Alastray is still an outlaw, and Kinita is engaged to marry the village sheriff.
As the villagers prepare for a final showdown with the Indians, Alastray must confront his past and decide whether to continue living as an outlaw or stay and fight with the people he has come to love. The film concludes with an epic battle between the villagers and the Indians, with the fate of San Sebastian hanging in the balance.