The year is 1492. Sixteen-year-old Titus Devere is thrown out of his religious order after proving that a divine revelation (blood streaming from a religious icon) was a fake, using his knowledge of Moorish science. He is brilliant and gorgeous but, cast as a heretic, he is sent to the Vatican in Rome where he expects to be punished or executed. Instead he is recruited into a secret order investigating strange occurrences across Europe. Known as The Order of the Dragon, it is headed up by a mysterious man with a tattoo of a coiled dragon eating its own tail on his arm.

Titus is sent to investigate an abbess who has been accused of witchcraft, alongside her slave and Moorish half-sister, Ishrak. The abbess, Ygraine, is actually a fifteen-year-old girl who has been shut up in a nunnery by her brother after her father's death, to ensure that she cannot inherit any of the family estate. Ygraine is a reluctant nun and manages to escape the abbey with Ishrak, though no one can work out how they did it. Titus is intrigued - could they really be using witchcraft? He follows their route and ends up linking up with them on their travels.

Titus and Ygraine find themselves attracted to one another, despite the conventions of the time. They travel across France, Switzerland, and over the Alps into Romania. En route they encounter alchemists, poisoners, inquisitors, purported witches, and more - ending up at the castle of real-life historical figure VladDracul (meaning Dragon in Latin).