Aidan, a ninth century Irish monk, is chosen to join a quest to the farthest reaches of the known world - the glittering city of Byzantium - there to present the Holy Roman Emperor with the magnificent illuminated Book of Kells. Separated from his fellow pilgrims, Aidan undergoes various exotic adventures, including capture by and life with Vikings, political intrigue in the Byzantine court, enslavement in a caliph's mine and loss of his all-important faith in God. Lawhead is a Christian writer, and here the Christian themes are integral and well developed; he also shows a keen and sympathetic eye for the values and cultures of non-Christians.