By day Eustaquia "Kiki" de Sonza and Ana Lezama de Urinza are proper young seventeeth century ladies. But when night falls, they trade in their silks and lace for swords and muskets, venturing out into the vibrant, bustling, crime-ridden streets of Potosí, in the Spanish Empire's Viceroyalty of Peru. They pass their time fighting, gambling, and falling desperately in love with one another. Then, on the night Kiki's engagement to the Viceroy's son is announced, her older brother—heir to her family’s fortune—is murdered. The girls immediately embark on a whirlwind investigation that takes them from the lowliest brothels of Potosí to the highest echelons of the Spanish aristocracy.