Catherine of Siena is one of the most intriguing and explosive saints in Church history. A young laywoman with almost no education, she became renowned for her intense mystical experiences, inspired preaching, and scathing criticism of corrupt political and ecclesial authorities. She is even recognized today as a Doctor of the Church--the only layperson to ever receive the title--yet comes across to us more as an apostle than an intellectual. Her work is like Aquinas' Summa set on fire. But for all the fascination with Catherine, the distinguishing feature of her life has received surprisingly little attention: her preoccupation with freedom. Catherine had a keen sense of the "unspeakably crazy" love of God and the liberating power of his mercy. But she also knew the terrible bondage of sin--and the necessity of facing our own inner darkness if we are to overcome it. She had a passion for leading those enslaved by fear and oppression to self-knowledge in God--and ultimately, to true freedom. It is this "fire" that inflames almost every page she writes. In this profound book, the Irish Dominican poet and writer Fr. Paul Murray draws us into the fire of this great mystic's love for God and humanity, reading her life and teaching not only in light of Dominican spirituality, but also the writings of Renaissance philosopher Giovanni Pico della Mirandola and the modern psychologist Carl Jung. What results is a portrait of a preacher of freedom who speaks to us, even today, with compelling authority.