A blacksmith's rise to wealth and power is jeopardized by his son's Christianity and the eruption of Vesuvius.

After his wife and son are injured by a runaway chariot and later die because he has no money to pay for a doctor, an embittered Pompeiian blacksmith, Marcus, dedicates himself to a career as a well-paid gladiator. Although he never relishes killing his arena rivals, Marcus soon becomes the most successful fighter on the circuit, earning substantial sums in the process. His life changes, however, when he meets Flavius, the seven-year-old son of a defeated opponent, whom he adopts. Eventually Marcus is forced out of the arena and must support Flavius through the odious but lucrative job of slave and horse trading. Before leaving on a horse buying trip to Judea, Marcus befriends a Greek soothsayer, who prophesies that Flavius will go to strife-ridden Jerusalem and meet "a great man" and that Marcus will be confronted with a life-altering choice between success and failure. Marcus, believing that the great man is Pontius Pilate, takes Flavius to meet the ruler, who offers Marcus a job stealing horses from his desert enemy. Although the raid is successful, Flavius is thrown from a horse and nears death, but is cured miraculously by a stranger known only as "The Lord." Marcus pledges his dedication to the stranger, but when another follower later begs his help to save the prophet from crucifixion, Marcus chooses to save his ill-gotten gold instead. Many years later, Flavius, who is haunted by dim memories of the man who had once cured him, rejects his father's plans for him and devotes himself to liberating runaway slaves who are destined for Marcus' deadly arena. Caught with the escaping slaves, Flavius is sent to fight in the arena, in spite of Marcus' pleas and bribes for his freedom. At the start of the battle, however, Mt. Vesuvius erupts, and once again, Marcus is given the choice between saving his wealth and human lives. After tossing away his coveted gold, Marcus finally sacrifices his own life to rescue Flavius and his band of runaway slaves. As Marcus' soul ascends to heaven, it is greeted with open, forgiving arms by the spirit of the doomed prophet, Jesus.