Although born to rule, Aidan lives as a scribe in a remote Irish monastery on the far, wild edge of Christendom. Secure in work, contemplation, and dreams of the wider world, a miracle bursts into Aidan's quiet life. He is chosen to accompany a small band of monks on a quest to the fabled city of Byzantium, where they are to present the beautiful and costly hand-illuminated Book of Kells to the emperor of all Christendom.

During this expedition by sea and over land, Aidan becomes, by turns, a warrior and a sailor, a slave and a spy, a Viking and a Saracen, and finally, a man. He sees more of the world than most men of his time, becoming an ambassador to kings and an intimate of Byzantium's fabled Golden Court. And finally, this valiant Irish monk faces the greatest trial confronting any man in any age: the command of his own destiny.