An alcoholic priest, whose name the reader never learns, roams the countryside of 1930s Mexico, ministering to the poor despite the fact that the government has outlawed Catholicism. The priest is a shell of his former self, racked by guilt over his many sins. He performs baptisms, communions, and last rites for the impoverished people of a small town in the state of Tabasco, who hold on to their faith despite the religious ban.
The priest moves on to another town, because his adversary, The Lieutenant, is searching for him. In this town the priest encounters the daughter he had fathered illegitimately while he was still a parish priest -- before the Church was banned. He is nearly captured by the lieutenant, who rounds up a group of men and asks them to turn in the priest. But no one informs on him, and the lieutenant, unaware that he has the priest in his grasp, lets the group go.
The priest returns to the capital city in disguise, planning to say a mass that night. But he is arrested for possessing liquor, also outlawed. He has another encounter with the lieutenant while in jail, and again his nemesis does not know his face.
He is freed, but without money or food, the priest stumbles from one hiding place to another, growing tired and weak. Finally, he is lured into a trap by a man seeking a priest to hear a dying man's confession. The man refuses to repent and dies, at which point the lieutenant appears and arrests the priest. The priest is executed by firing squad the next day.
Elsewhere in the town, a mother is reading a story to Juan, her young son, about a Christian martyr killed for his faith long ago. Juan asks if the man killed that day is a martyr as well. His mother agrees, and the boy grows despondent that the "last" priest has been killed. That night, a stranger knocks on their door. It is another priest, fleeing from the police. The boy, heartened, opens the door and takes in the priest.
Best scene in story:
When the boy sees the second priest at the end of the novel, he practically throws himself at the priest's feet, begging him to enter his home.
Opinion about the main character:
The priest is drowning in shame and guilt over the sins he's committed, the sins he knows he will commit, and those he's only thought about committing.