This is an alternate history story set at the end of the Roman empire. The empire has split into three competing segments. In the west, the Gallic empire, poorer and weaker than the East, has recruited the aviators to patrol the frontier and bring warning of invasion. Alcuin, from Britain, is one of the best. Now Gaul faces its biggest threat yet. The Arabs have humiliated the Eastern Empire, conquered North Africa, and invaded Spain. Their raids threaten the heart of the empire. Then Gaul's best general instructs Alcuin to deliver a sealed message to the Pope. Then Alcuin discovers the letter's shocking secret. The aviators are supposed to stay out of politics. Alcuin understands the reason for that order. He fears that his mission could be regarded as treason. In the Eastern Empire, Theodora is an orphan, trapped in a convent. She dreams of escaping to the emperor's court in Constantinople, a place where people contemplate exciting things - including treason. Alcuin's travels take him from Gaul to Constantinople and Muslim Spain, both richer than Gaul. Then he returns to his barbaric homeland, Britain