An unsolved murder. A banker's son goes missing. A case for Sherlock Holmes. Paris, at the end of the 19th century: When a cash courier is found hanged in the attic of the reputable banking house Beaumont Frères, the police suspect suicide and close the case. Years later, Maurice Beaumont, junior partner of the firm, disappears without a trace while on vacation - another mystery with no solution. And all the while the brutal murder of a rag-and-bone man, contemporaneous with the hanging, raises no suspicions. However, precisely this event could hold the key to the solution of the other cases. Sherlock Holmes and Dr. Watson travel to the French capital; in the depths of the Paris police archives they stumble upon a clue that leads their investigation in a new direction...