The king at the edge of the world

the long version

"Queen Elizabeth's spymasters recruit an unlikely agent--the only Muslim in England--for an impossible mission." -- 1601. Queen Elizabeth I is dying. With no heir for the kingdom, potential successors secretly maneuver to be in position when the inevitable occurs. The leading candidate is King James VI of Scotland, but there is a problem. The queen's spymasters fear that James' claim to be a Protestant are untrue. If he secretly shares his family's Catholicism, then forty years of religious war will have been for nothing, and a bloodbath will ensue. It falls to Geoffrey Belloc to devise a test to discover the true nature of King James's soul. Belloc enlists Mahmoud Ezzedine, a Muslim physician from the Ottoman Empire, as his undercover agent. -- adapted from jacket