Marquise De Ganges

The Marquise de Ganges is part of Dumas' true crime novel series Celebrated Crimes, Vol. 8: Part 3: 

The assassination of Diane de Joannis de Chateaublanc (the Marquise de Ganges) is a fitting tale to conclude Dumas’ celebrated crimes series. This event was as gruesome as it was brazen and, before the final dagger strokes, both the assassins and the assassinated had become embroiled in high-profile intrigues. As a result, it sent reverberations through common and court societies across Europe for decades.