Casca returns from Khitai along the Silk Road heading west and bumps into a party of Huns that had killed a group of Kushanites, leaving one survivor, a young man who resembles a former friend, Jugotai. Casca frees the young man who turns out to be Jugotai's son Shuvar and kills a few Huns before escaping westwards into Persia. There he makes his way to the city of Nev-Shapur and as he carries letters from the Chin Emperor Tzin he is received as an emissary. Although Rome and Persia are old enemies Casca is accepted by the king, Shapur II, as a loyal subject and is enrolled into the armed forces as a commander.
Unfortunately the Vizier to Shapur is a sly man named Rasheed who is a member of the Brotherhood of the Lamb and the sect begins a close watch on him. Rasheed is a fanatic and wishes nothing more than to destroy Casca and begins to undermine Shapur's confidence in him. Casca meanwhile has befriended an Egyptian called Imhept who has been contracted by Shapur to survey the irrigation system of Persia and recommend improvements. Casca then commands a Persian army that destroys an invading Hun tribe and is rewarded by a grateful Shapur.
Casca then falls for a slave girl from Armenia called Anobia and she falls in love with him and she is freed from servitude and becomes mistress of the house. Shapur is glad of this as it means he has leverage on Casca if the need arises. Then Casca is sent with a Persian relief force to rescue Kushan, an ally of Persia, from the ravages of an invading Hun army. After crossing the mountains Casca and his army joins forces with Jugotai and Shuvar's besieged forces and together they destroy the Huns but at the price of Jugotai's death. On their return Casca is still depressed by the death of his old friend.
By this time Shapur's mind has been poisoned by Rasheed and decides to arrest Casca. The prisoner is brought to the king and proof of his immortality - a freshly made wound that closes immediately - is all they need to be convinced by Rasheed that Casca is an agent of Ahiraram, the evil god of the Persians. Casca is sentenced to death by burning. As he is being burned he knocks himself out and is unaware that Imhept has rushed to his side and kicks away the burning logs from his body. He calls on a favor from Shapur to allow him Casca's body. Shapur, convinced the Roman is dead, agrees.
Over the next few weeks Imhept tends the burned body and gradually Casca returns to fitness, recovering at a rate the Egyptian finds incredible. Eventually Casca is fit enough to leave and gratefully thanks the Egyptian for what he has done, before travelling west towards the lands of Rome.
At the next meeting of the Brotherhood of the Lamb the elder decides to stop any further near disasters by having Rasheed picked as the 'sacrifice' for the re-enactment of the crucifixion. Elder Imhept is much relieved he has saved the only known route back to Jesus.
Shapur II's long reign in the fourth century AD (309-379) was one of the most successful of all Sassanid rulers - Sadler describes vividly the means by which the 17-year old king came to power and Shapur was to rule for seventy years. In the book references were made to the current reign of Constantine (312-337AD) so the book probably covered the later part of that reign and beyond. The Huns did cause many problems to Kushan and Persia during their long trek westwards which was to culminate in the reign of Attila and after Shapur's death were to severely weaken the Sassanid dynasty's empire. Sadler demonstrates in this book his knowledge of Zoroastrian religious ceremonies and gods and throughout his novels continues to concentrate on religion, war and in many instances Oriental cultural influences, perhaps a consequence of his time in the US armed forces in Vietnam.