Katherine of Valois was born a princess, the daughter of King Charles VI of France. But by the time Katherine was old enough to know him, her father had come to be called “Charles the Mad,” given to unpredictable fits of insanity. The young princess lived a secluded life, awaiting her father’s sane moments and suffering through the mad ones, as her mother took up with her uncle and their futures became more and more uncertain. Katherine’s...