The story tells the life histories about Saints Peter and Paul of Tarsus after the crucifixion of Jesus, and their individual fates in old Rome in the time of the persecution of Christians.
Events in the New Testament Book of Acts by Luke and in the Ecclesiastical History of Eusebius are dramatized and interwoven with the contrasting histories of political intrigues in the public and private lives of the Caesars from Tiberius through Nero related in The Twelve Caesars by Suetonius, together with the fictional drama of the lives of two Jews and two Romans: Caleb the Zealot and his sister Sarah, and Julius Valerius the Imperial Guard and Corinna the patrician woman who has chosen to be a gladiator.
Julius Valerius, having met Sarah on Sejanus' estate, has fallen in love with her, and when she is put on the slave block to be sold as part of an imperial fund-raising effort he, with the financial help of his parents and additional funds provided by Aquilla and Priscilla, Jewish tent-makers, buys her for himself and frees her to become his wife.
Valerius and Caleb participate in the plot to assassinate Caligula, and the stammering Claudius (found hiding) is hailed as the new Caesar.
The dramatization of the persecution that follows includes the inverted crucifixion of Peter, the beheading of Paul, and the preparation of Christian children for the arena being dressed in fresh lambskins and led out to be torn to pieces by Roman war dogs.
During public announcements of more entertainment to come, Valerius enters and grieves over the death of his daughter, only to find afterward that she is still alive and was never in the arena.