Sherlock Holmes's latest case takes him to the heart of Paris, in pursuit of Marguerite Hardy - a mysterious Frenchwoman who fled her comfortable English home when she received a strange letter. Desperate for her safe return, her husband begs for Holmes's help. But Holmes's investigations will take him and his cousin, Henry Vernier, into a world of theft, seduction and betrayal - and uncover a secret that has been buried for over twenty years.