The film tells the life of Saul, a merchant of Tarsus, who became Saint Paul, the first great missionary of Jesus.

Shortly after getting Saint Stephen arrested and stoned(in the Italian version, this was Saint James), while he is going towards Damascus with the intention of persecuting the believers of Christ, who have gathered there, during a storm he hears the voice of Jesus crying: "Saul, Saul, why are you persecuting me?", and that makes him fall from his horse, while a flash of lightning suddenly takes away his sight. Having converted and cured of blindness, with the new name of Paul he goes to Rome, and on the Via Appia, he enters the catacombs, where a slave of the emperor and a soldier, newly converted to Christianity, are baptized. During the burning of Rome, Paul is arrested. In the arena, Nero inspects the Christians destined to be killed hanging like human torches on crosses. Paul is brought out of the dungeon where he was locked up because the Romans fear that he will bring the wrath of the Christian God upon them. Shortly after he is killed. Christians bring flowers and palm trees to his grave at the edge of the road.

The movie contains two parts, one before and one after the conversion of Paul.