In 1474, when most women were almost powerless, twenty-three-year-old Isabella defied a hostile brother and a mercurial husband to seize control of Castile and León. Her subsequent feats were legendary. She ended a twenty-four-generation struggle between Muslims and Christians, forcing North African invaders back over the Mediterranean Sea. She laid the foundation for a unified Spain. She sponsored Columbus’s trip to the Indies and negotiated Spanish control over much of the New World. She also annihilated all who stood against her by establishing a bloody religious Inquisition that would darken Spain’s reputation for centuries. Whether saintly or satanic, no female leader has done more to shape our modern world. Yet history has all but forgotten Isabella’s influence. Using new scholarship, Downey’s luminous biography tells the story of this brilliant, fervent, forgotten woman, the faith that propelled her through life, and the land of ancient conflicts and intrigue she brought under her command.