This book examines the active political life of Luisa Carvajal y Mendoza (1566–1614), a poet and mystic who renounced her noble birthright for an ascetic, spiritual life. Historian Freddy Cristóbal Domínguez draws on Luisa’s autobiographical writings, letters, and poetry to explore how piety and politics interacted in early modern Europe. He recounts Luisa’s remarkable decision to leave Catholic Spain to work as a missionary in Protestant England. She sought to help the afflicted Catholic community there and fulfill a vow of martyrdom. Domínguez argues that, though Luisa was a “holy” person—twice imprisoned for her beliefs—her spiritual goals were fundamentally intertwined with politics. Not incidentally but purposefully, she sought to influence Spain’s foreign policy, advised political figures, and engaged in polemical debates and performances against Protestants in England. As the first book to focus primarily on Carvajal y Mendoza’s politics, this multifaceted, innovative work expands our understanding of the role of laywomen in public life in early modern Europe. It also explores the roles of both Spain and England in shaping Luisa de Carvajal y Mendoza’s story and how she emerged as a political actor in multiple public spheres.