The book tells the story of a young English boy, Rob Cole, in the 11th century who becomes an apprentice to a barber-surgeon. Rob's ambition to become a physician takes him across Europe and into the heart of the Muslim world, a journey fraught with danger and discovery. He disguises himself as a Jew to study at a school that does not admit Christians. The narrative is a captivating mix of history, science, and adventure, highlighting the protagonist's perseverance and the state of medical knowledge during the Middle Ages.

The novel is a sweeping historical epic that takes readers on a journey through the ancient world, as seen through the eyes of a fictional Persian diplomat. The protagonist, who serves under King Darius and later his successor Xerxes, engages in philosophical and theological debates with some of the era's most influential figures, including Confucius, Socrates, and the Buddha. His travels and experiences provide a panoramic view of the political and cultural landscapes of the time, exploring the nature of power, belief, and the human condition. The book blends real historical events and personages with a richly imagined narrative, offering a unique perspective on a formative period in human history.