Classic mystery novel in the original French. Number 6 in the series Les Habits Noirs. According to Wikipedia: "Paul Henri Corentin Feval, (29 September 1816 - 8 March 1887) was a French novelist and dramatist. He was the author of popular swashbuckler novels such as Le Loup Blanc (1843) and the perennial best-seller Le Bossu (1857). He also penned the seminal vampire fiction novels Le Chevalier Tenebre (1860), La Vampire (1865) and La Ville Vampire (1874) and wrote several celebrated novels about his native Brittany and Mont Saint-Michel such as La Fee des Greves (1850). Feval's greatest claim to fame, however, is as one of the fathers of modern crime fiction. Because of its themes and characters, his novel Jean Diable (1862) can claim to be the world's first modern novel of detective fiction. His masterpiece was Les Habits Noirs (1863-1875), a criminal saga comprising eleven novels."
