In 1666, an astronomer makes a prediction shared by no one else in the world: at the stroke of noon on June 30th of that year, a solar eclipse will cast all of Europe into total darkness for four seconds. This astronomer is rumored to be using the largest telescope ever built, but he is also known to be blind—both of his eyes were plucked out under mysterious circumstances. Is he mad? Or does he, despite this impairment, have an insight denied the other scholars of his day? These questions intrigue the young Gottfried Wilhelm Leibniz—not yet the world-renowned polymath who would go on to discover calculus but a nineteen-year-old whose faith in reason is shaky at best. Leibniz sets off to investigate the astronomer’s claim, and in the three hours before the eclipse occurs—or fails to occur—the astronomer tells the scholar the story behind his strange prediction: a tale that ends up encompassing kings and princes, family squabbles, insanity, art, loss, and the horrors of war.