Rome in Emperor Nero’s times is steeped in crime and debauchery. Marcus Vinicius, a young and beautiful warrior, comes to his uncle Gaius Petronius, who is a writer, aesthete, connoisseur of luxury and pleasure, and the approximate of Nero. The young man says that, upon returning to Rome from the war against the Parthians, he injured his hand and has been taken to the house of the white-haired commander Aulus Plautius for care.
There Vinicius was captivated by a young Ligia, the daughter of the king of the Ligians, who lived in far northern forests. At home, the Ligians called her Galina. She came to Rome as a young hostage and grew up in the house of the noble Aulus and his faithful, virtuous wife Pomponia. Treating Ligia as their own daughter, they raised her pure and chaste. She was nothing like the debauched women of Rome. Pomponia is said to be a Christian, but Petronius does not believe it, as Christians are said to be terrible villains, and Pomponia’s face seems to radiate light, which cannot be villainous in any way.
In the house of Aulus Vinicius, Vinicius uttered many fervent words to Ligia, and the girl's heart burnt with reciprocal feeling. Now Vinicius is ready to marry Ligia, but he does not understand one thing: why she draws fish on the sand. Petronius tells Nero that Vinicius fell in love with the weedy hostage Ligia, and the Emperor promises Petronius to take Ligia to his palace and give her to Vinicius.
Ligia is accompanied by the giant Ursus to the palace. Ursus is a Ligian who came to Rome with the little princess Ligia and, as she has, became a Christian here. In the evening, Ligia is led to the feast, trembling in fear. Fortunately, Ligia takes a seat next to Vinicius. However, soon intoxicated by wine and passion, Vinicius begins passionately kissing the beautiful Ligia, whispering that tomorrow Nero would give her to him. Ursus comes to the rescue, throwing Vinicius away and taking the scared girl from banqueting halls. Ligia is crying, for she does not want to become the concubine of Vinicius. Better poverty than luxury and dishonor! Ligia decides to run away.
After learning about the disappearance of Ligia, Vinicius kills an old servant. For the first time in his life, someone has dared to oppose the wishes of the young patrician. Mad with love and despair, Vinicius looks for Ligia. Petronius, sympathizing with his nephew, is ready to give him his beautiful slave girl, golden-haired Greek Eunice. But she so passionately pleads him not to send her out of the house that Petronius realizes that she is in love with himself. Eunice’s devotion touches his heart. Eunice brings the crafty Greek Chilo, a drunkard, swindler, a spy, and informer, to find Ligia. Upon learning that she drew a fish on the sand, Chilo, like a monkey and the fox at the same time, goes in search of her.
Chilo soon discovers that the fish is a secret sign of the Christians. Pretending to be a Christian, Chilo penetrates into their environment and meets the physician Glaucus, whose family he once gave up to robbers. Now Chilo fears that Glaucus might recognize him and tries to incite another Christian on the physician. Chilo tells this other Christian, simple-minded strongman Urban, that Glaucus is Emperor Nero's spy. By the way that the giant shudders when Chilo accidentally mentions the name of Ligia, the cunning Greek understands that Urban is actually Ursus.
The apostle Peter comes to Rome. All the Christians in the city are going to his sermon that night. Chilo brings Vinicius there, who hopes to meet Ligia. The apostle Peter struck Vinicius with his simplicity and grandeur. His face lit up by the power of Peter's persuasion, which is inherent only to the truth. However, Peter's sermon negates all of Vinicius’s life. The story of the crucifixion and resurrection of Christ shakes the young patrician, and he realizes that the Christian Ligia would never be his concubine. When Vinicius sees Ligia in the crowd, he admires the beauty of the girl and realizes that his strength and courage against her faith is nothing.
Having followed Ligia after the sermon, Vinicius bursts into her home and tries to carry her away, but Ursus brings down his mighty fist on Vinicius’s head. Glaucus looks after Vinicius in Ligia's closet. Ligia herself tenderly cares for him. Vinicius is happy, and wanting to stay with his beloved, he decides to stay with the Christians. Then he sends for Chilo, the only one who knows where he is. After seeing Chilo, Glaucus recognizes him as the villain who previously destroyed his whole family and as the old man who incited Ursus on Glaucus. Chilo howls with terror, but the apostle Peter appears and lets Chilo go. Glaucus and Ursus then forgive him.
Shaken, Vinicius ponders over the kindness and charity of the Christians. Then he falls into oblivion, and he fancies that Ligia leads him to the place where the sun shines. A few days later, Vinicius feels that his deep passion had been replaced by true love, but conflicted Ligia, not daring to love a pagan Roman with a wolf heart, decides to leave him.
Vinicius returns home, but everything seems to be empty. He yearns for Ligia and often reminisces about the wonderful man he met while he was with the Christians, Paul of Tarsus. Vinicius's soul is changing. He considers the debauchery of the Roman nobility disgusting, and at a luxury feast, he rejects the harassment of Empress Poppaea. She disappears laughing sinisterly.
Vinicius dreams of Ligia. Suddenly, ragged Chilo comes to him and says that once again he has tracked the Christians. Enraged by Chilo's meanness, Vinicius orders that he be whipped. Then, moaning Chilo leads the young man to the new home of the apostles. There Vinicius asks Peter and Paul for Ligia’s hand and promises that he will try to understand and accept the teachings of Christ. Delighted Peter blesses the lovers.
The maddened Nero dreams about the great fire, and soon the Emperor's henchmen set fire to Rome. Looking for Ligia, Vinicius, in despair, rushes through the flaming city. With difficulty, clambering in a smoldering tunic from the sea, Vinicius stumbles upon Chilo, who advises him to seek Ligia and Peter in one of the underground chapels of the Christians. Vinicius hurries back and sees crowds of desperate people being calmed down by the tender words of the Apostle Peter. Noticing Vinicius weakened from the horrors, Peter leads him to Ligia. Falling to his knees, the Vinicius warmly thanks the Lord, and Peter, who loved Vinicius with all his heart, baptizes him in the poor hut of a digger.
People are filled with anger. To protect the Emperor and themselves, the patricians spread a rumor that the Christians had set fire to the city. To punish the "evildoers", Nero was going to arrange a spectacle that would be remembered for centuries. Poppaea secretly leads Chilo to the emperor. He is ready to give up all the Christians to Nero, especially Ligia and Vinicius. Chilo takes his revenge for being whipped.
Petronius warns his nephew Vinicius that the persecution of the Christians is being prepared, but Vinicius doesn't have time to save Ligia. She was taken away to prison. Petronius understood why this happened. This was the revenge of Poppaea, whom Vinicius rejected for Ligia. Vinicius himself was not arrested because Poppaea wanted to enjoy his suffering by torturing Ligia in front of his eyes.
The mob is engulfed with bloodlust. Christians are thrown into prison with a thirst for martyrdom. The suffering of Vinicius exceeds human forces. Then St. Peter receives a revelation: in this city of Satan, Christ wants to establish his capital.
With enlightened faces, the Christians go to face death and in terrible pain, they die in the arena. Chilo, sitting in luxurious robes next to Nero, whispers, "They see their resurrection!" and falls unconscious. The executions continue. Vinicius, disguised as a gravedigger, gets into the terrible prison and spends three days with Ligia. Their souls have been cleansed from all earthly things. Vinicius decides after Ligia's death to admit that he is a Christian and to follow his beloved.
Christians are being burned on poles, hundreds of which cover the emperor’s gardens. On one of the poles, Glaucus looks at the grizzled Chilo and croaks, "I forgive!" Chilo, shocked, turns from a miserable man into a grand old man and shouts, "Christians are innocent! Nero is the incendiary!” These words instantly spread over Rome, and Chilo, having repented his sins, is baptized in a dark alley by the apostle Paul. Chilo is soon captured, but no amount of torture can force him to recant his words. The Romans rip off his tongue and let him be torn up in the arena by a bear. However, the beast doesn't touch him. With an enlightened face, tortured Chilo emits spirit.
The emperor decides to give Vinicius a "merry wedding." White as chalk, Vinicius sees Ursus pushed into the arena, and then a huge tour, to whose horns Ligia, naked, is tied. Ursus grabs the tour’s horns and cracks his neck. The crowd roars with delight, and Nero, fearing the crowd, gives Ligia and Ursus life and freedom.
In the house of Petronius, Ligia and Vinicius beg long-suffering Peter to leave Rome. Peter says, "I must go after my flock," but the Christians still manage to convince him that he should sow the seeds of truth in other cities and towns. Peter leaves Rome, but on the Appian Way, Christ appears to him. "Quo vadis, Domine? (Where do you go, Lord? - Latin)" asks Peter, and Peter hears in reply, "If you leave my people, I am going to Rome for a new crucifix."
Shaken Peter returns to Rome. Soon, the apostles are thrown into prison, but when Peter is beaten to death, he walks like a winner. Looking around Rome, Peter whispers, "You are redeemed, you're mine!" Equally quietly, Paul dies on the same day at the death penalty.
Vinicius and his wife Ligia live peacefully in Sicily, and they love each other. They believe in Christ and are immensely happy.
However, Petronius is doomed. Nero is sinking deeper into his infamous lewdness, and now Petronius only hinders the emperor. Nero plans to send Petronius a death sentence, but Petronius decides to play one last joke on Nero. At the feast of luxury, surrounded by friends, Petronius cuts his veins. With him, his slave-girl Eunice dies, refusing to live without a loved one. Before his death, Petronius sends Nero a mocking letter in which he had written that he was ready to forgive all of Nero's offenses and murders, but he deeply despised Nero for his bad verses. Guests look at the beautiful, marble-white, lifeless bodies of Petronius and Eunice, understanding that the only things that still remained in the old world, poetry and beauty, have been killed.
Nero becomes completely mad. Finally, mutinous legions proclaim Galba the new emperor. With the words, "What an artist dies!", Nero puts a knife to his throat. However, he cannot pull through because of fear, so his slave helps his master die with a swift stroke.
From the soil soaked with blood and tears, the seeds of Peter quietly but steadily rise up.
Nero has long been left in the past, and St. Peter's Basilica at Vatican hill now reigns over Rome and over the world. Near the ancient Porta Capena stands a small chapel with a partly vanished inscription: "Quo Vadis, Domine?"
