The memoir relates Julian's life from the time so many members of his family were purged by his cousin, the emperor Constantius II (whom he succeeded on the throne), his "exile" to libraries as a child, and his subsequent negative childhood experiences with Christian hypocrisy and conflict over dogma (see Arianism).

He also comes to know some of the early Church Fathers in their formative years, including the agreeable Basil of Caesarea and the abrasive and dishonest Gregory of Nazianzus.

Nonetheless, Julian takes the opportunity to outline his arguments against Christianity, and to lay out his vision for reforming and restoring Roman civic life.

His reforms are under way when, in spite of his own faith in prophecy, Julian undertakes an ill-omened campaign to reclaim Roman Mesopotamia from the Sassanid Empire.

The rest of the novel consists of field dispatches and diary entries detailing Julian's campaign, with commentary by Priscus and Libanius's reflections.

Initially, Julian is extremely successful (in spite of his relying on Xenophon's dated Anabasis for geographic details of the region), reaching Ctesiphon and defeating the Persian emperor in several decisive battles.

Indeed, Julian's dispatches begin to show delusion on the part of the emperor, and in spite of his steadily eroding grasp of reality and his own limitations, he presses on until a near mutiny of his soldiers.

Not long after, during the return to Roman territory, Julian rushes to fight off a Persian attack on the line, eschewing his armor, since his aide Callistus has not repaired its broken straps.

Julian returns to camp mortally wounded, and in spite of the efforts of his physician and friend Oribasius, he dies without picking a successor.

The novel ends with Libanius's sending a letter to the emperor Theodosius seeking permission to publish Julian's memoir; it is denied.

Lamenting his ill health, Theodosius's politically motivated proscription of traditional religion, and the end of intellectual culture and its replacement by widespread religious violence and intolerance, Libanius meets John Chrysostom, his former best student, giving a sermon at a Christian church.

In closing, Libanius writes, prophetically, that he hopes the coming collapse of reason and the Roman world will be only temporary, likening the dying of the Empire to that of his oil lamp, and expresses the hope that reason and 'man's love of light' would one day bring back the prosperity, stability, and intellectualism of the pre-Christian empire.

The death of Julian, and the reasons for it, are based on the opinion of Libanius and Vidal's interpretation of a very short but vital lacuna in Ammianus' history as due to active censorship rather than the ravages of time.