Hadassah, the Christian heroine of the first two books of "Mark of the Lion", is martyred for her faith early in the book. Thus begins a new chapter in the "Mark of the Lion" saga, this time with Atretes and another young Christian woman, a widow named Rizpah. Atretes' baby by Julia was not killed after all, Hadassah tells Atretes; she had rescued the child and given him to the apostle John in Ephesus. Desiring his son, Atretes finds the apostle and learns that John has given the baby to Rizpah. Determined to get his son back, he gets more than he bargained for when Rizpah, who loves the babe as her own, refuses to leave.
Restless with his newfound freedom after ten years of being trained to fight and act like an animal in the arena, Atretes desires to return to his homeland. But he does not know the way home, and lacks the money for such a long journey (having spent all his fortune on a villa near Ephesus). His former instructor as well as the many amoratae (gladiator "groupies" or fans) would gladly see him return to the arena, the only thing he really knows. In desperation Atretes finally accepts help from Rizpah.
Primarily a travel-focused book, As Sure as the Dawn includes several maps showing the different parts of the long trip. The story, likewise, is actually composed of four distinct segments: Atretes' life before leaving Ephesus, followed by the first leg of the journey, by sea to Rome. Later, Atretes and Rizpah, along with a retired, Roman centurion named Theophilus, continue the journey by land, north through Italy, over the Alps and into barbarian country, finally arriving among the Chatti tribe, where the last part of the story takes place.
Along the way, Atretes fights against the continual presence of the Christians, especially despising Theophilus, a Roman: for he also hates Rome and anyone or anything affiliated with Rome. His pride and anger continually get him into trouble, leading up to very tense and exciting scenes in the capital city itself, when it appears indeed that Domitian will find Atretes and send him back to the arena. Many times throughout the adventures, Atretes tries Rizpah's patience (and that of the readers) with his foolish, stubborn ways, while in spite of everything, Atretes and Rizpah feel increasingly attracted to each other.
Some parts of the novel seem to drag too much, overloading the reader's level of frustration while holding back too much on Atretes' gradual change. Will he ever learn, will he ever change? Yet just when, seemingly, the story has gone far enough in one direction, the plot abruptly shifts, and slowly the characters grow and mature from their experiences.
Though overall a historical fiction novel, the last part in particular resembles more of a "spiritual warfare" story in the style of Christian author Frank Peretti. A tale of its own (quite different from the earlier pages of As Sure as the Dawn), this story involves the dark spiritual forces of the pagan Chatti. Like other nations untouched by the gospel (even with today's primitive savages in dark parts of the world), the real question is: which god is more powerful? The Chatti's power-obsessed, demonic priestess, a young woman named Anomia, opposes Atretes' and his new religion and tries to rally the people to their native god, Tiwaz.
Though primarily a combination romance and spiritual warfare story, the historical setting of early Rome brings out interesting details of the Roman Empire of the time (A.D. 80). Reference is made to the Romans' destruction of Jerusalem in 70 A.D., along with mention of the more recent destruction of Pompeii by volcano (A.D. 79), which the ship passengers can observe along the coast of southern Italy. Also mentioned is the history of conflict between Rome and the Germanic tribes, and the Romans' practice of enslaving German captives (as in the case of Atretes). The Chatti were an actual Germanic tribe, a particularly difficult foe for the Romans, that also fought against the Hermunduri, another actual tribe mentioned in As Sure as the Dawn. The story is replete with several Roman words, such as triclinium, aureus (a type of coin), and the ludus; a glossary at the back explains the meanings of these and many other words of first-century Rome. Rizpah, Atretes, and Theophilus experience both the decadence of the Roman public baths and the peaceful, if not deathlike, hiding place of the catacombs, all bringing alive the world of Ancient Rome to modern-day readers.