This article reexamines the life of Luisa de Carvajal y Mendoza, a Spanish noblewoman who traveled to London in 1605 hoping to be martyred in service of the Catholic faith. By placing her at the intersection of a series of international, intra- and interconfessional tensions created by the sustained religious division of post-Reformation England, Carvajal emerges as a sophisticated political actor. She offers not only a unique account of female Catholic agency and opposition in early Stuart England, but also a lens through which to view the nature of religious identity and division in a period of Anglo-Spanish peace.