In the time of Jesus Christ, blacksmith Marcus (Preston Foster) is content with his life, beautiful wife Julia (Gloria Shea) and six-month-old son. However, when Julia and their child are run down by a chariot in the streets of Pompeii, Marcus spends the little money he has to pay for a doctor and medicine. Needing more, in desperation, he becomes a gladiator. He wins his fight, but in vain; his wife and child die.
Blaming his poverty, he becomes an embittered professional gladiator and grows wealthier with each victory. In one match, he kills his opponent, only to discover he has orphaned a young boy named Flavius (David Holt). Full of remorse, he adopts the boy and purchases a slave, Leaster (Wyrley Birch), to tutor him. However, the added responsibility makes him too cautious in the arena, and he is defeated and injured. The injury ends his second career.
When Cleon (William V. Mong), a slave dealer, offers him a job, Marcus is at first contemptuous, but eventually takes it. He raids an African village for slaves, where a father battles Marcus’ raiders until his young son’s life is threatened and he is forced to surrender. Marcus identifies with the father’s grief at being unable to protect his son. He stops slaving and turns to trading instead.
One day, Marcus rescues a fortune teller, who foretells that Flavius will be saved by the greatest man in Judea. Marcus and Flavius travel to Jerusalem to see the man that Marcus thinks fits that description: Pontius Pilate (Basil Rathbone), the Roman governor. At an inn along the way, a man tells him that the greatest man is staying in the stable (similar to the one in which he was born), but Marcus does not believe him.
On learning that Marcus was once a great gladiator, Pilate employs him secretly to lead a band of cutthroats to raid the chief of the Ammonites, who has been causing him problems. Marcus comes away with many fine horses and much treasure, but when he goes to see his son, he finds that Flavius has been thrown from a horse and is near death. With no doctors around, Marcus desperately takes the boy to a noted healer and begs for his help. The healer is Jesus, who saves Flavius’s life. When Marcus later reports back to Pilate with his share of the treasure, Pilate has sentenced Christ to death. The remorseful (as depicted in this film) Pilate is disheartened with guilt over his condemnation of an innocent man.
Marcus leaves the city quickly, but as his party is departing, one of the apostles recognizes him and begs him to rescue Jesus, carrying his cross through the streets, but Marcus refuses. As Marcus and Flavius leave Jerusalem, they see three crosses on Calvary behind them.
Years pass. Marcus has grown wealthy as the head of the arena in Pompeii. Flavius (played as an adult by John Wood) is now a young man. Flavius is haunted by the memory of the man who healed him, though his recollections are so vague that his father easily dismisses them as nonsense. One day, Marcus welcomes Pontius Pilate as a guest to his lavish home. When Flavius mentions his early childhood memories of a man speaking about love and compassion, Marcus assures him, as he has always insisted, that there was no such person. Pilate answers, “Don’t lie to him, Marcus. There was such a man.” Flavius asks, “What happened to him?”, and the still-remorseful Pilate answers, “I crucified him.” It is then that the memory of the three “crosses on the hill” comes flooding back to Flavius.
Unbeknownst to Marcus, Flavius has been secretly helping slaves escape from certain death in his father’s arena. However, he is arrested with a group of the runaways and sentenced to die. When he discovers what has happened, Marcus tries to free Flavius, but in vain. Flavius is herded into the arena with the others, but as the fighting begins, Mount Vesuvius erupts. As Marcus wanders stunned through the streets with the panic-stricken populace, he sees the jailer who refused to release Flavius trying to free his own son from the rubble. The dying man begs Marcus for mercy for his son. Marcus angrily refuses, but then remembers begging Jesus for mercy for Flavius and rescues the boy. Marcus sees his faithful servant Burbix (Alan Hale) leading a group of slaves carrying his treasure on litters. He orders them to use the litters to rescue the injured instead. As they get to a ship, Marcus sees that one of those saved is Flavius and offers a prayer of thanksgiving. The prefect and his men try to get through a gate to take the ship for themselves. Marcus holds the gate shut, giving the boat enough time to get away at the cost of his life. He has a vision of Christ reaching out to him just before he dies.