Paris, 1534. A student at the Catholic Collge de Montaigu, serving as a courier for the Inquisition, is murdered by members of an extreme Lutheran sect for the packet of letters he is carrying. His friend and fellow classmate, Amaury de Faverges, the illegitimate son of the Duke of Savoy and an expert in astronomy and natural science, is recruited as his replacement and promised a decree of legitimacy if he can uncover the secret that threatens to overturn Catholicism and the reign of Franois I.

Working undercover, Amaury journeys south to the liberal court of the king's sister, Marguerite of Navarre, the alleged heart of the conspiracy. The deeper he probes, the more Amaury is forced to confront his own religious doubts. And when he discovers a copy of Copernicus's shocking manuscript showing the sun at the center of the universe, he knows the path he must follow.

Replete with characters and events from history, from the iconoclastic Rabelais to the burning of heretics in Paris to preacher John Calvin and Copernicus himself, The Astronomer is a powerful novel of love and betrayal, and a thrilling portrait of what might well have happened at a hinge point in history when science and ancient religious belief collided.