In the late 16th century the greatest philosophers, alchemists, astronomers, painters, and mathematicians of the day flocked to Prague to work under the patronage of the Holy Roman Emperor Rudolf II, an emperor more interested in the great minds of his times than in the exercise of his immense power. Rarely leaving Prague Castle, he gathered around him a galaxy of famous figures: among them the painter Arcimboldo, the astronomer Tycho Brahe, the mathematician Johannes Kepler, the philosopher Giordano Bruno and the magus John Dee.

Fascinated by the new Renaissance learning, Rudolf found it nearly impossible to make decisions of state. Like Faust, he was prepared to risk all in the pursuit of magical knowledge and the Philosopher's Stone which would turn base metals into gold and prolong life indefinitely. But he also faced threats: religious discord, the Ottoman Empire, his own deepening melancholy and an ambitious younger brother. As a result he lost his empire and nearly his sanity. But he enabled Prague to enjoy a golden age of peace and creativity before Europe was engulfed in the Thirty Years' War.

Filled with angels and devils, high art and low cunning, talismans and stars, The Mercurial Emperor offers a captivating perspective on a pivotal moment in the history of Western civilisation.