In 17th-century Paris, Catherine Monvoisin reinvents herself as a sorceress to escape poverty when her spendthrift husband lands them deeply in debt. With the help of her prophetic visions, a grimoire given to her by a legitimate diviner, and a little grease from an unscrupulous mentor, soon the 19 year-old has helped a young Marquise become Louis XIV's royal mistress. Her reputation and prospects soar as she pits the noblesse against each other, until a charged rivalry with a young magician entangles her in all manner of darkness, including murder, deception, and possibly her own death.