Gloria is the fourth novel in The Sebastian Cycle quadrilogy of the Blood of Martyrs series, which deals with the persecution of Christians during the reign of Emperor Diocletian.

Twice Emperor Diocletian sends delegations to entreat Susanna to marry Emperor Maximian. Twice, she declines. Sebastian does not learn of the proposal until she is hauled to the palace as an imperial concubine.

Because Susanna has the audacity to rebuke Maximian for the massacre of the Theban Legion, she is condemned as a seditious revolutionary and executed.

Sebastian himself, betrayed by the apostate Torquatus, is arrested, whereupon he learns Susanna's fate. Before a firing squad, he is impaled with arrows and left for dead. But, incredibly, he survives.

Will Sebastian flee or avenge himself on the wicked Emperors?