Paris, 1878: Eccentric antiquarian Lord Littleby and his ten servants are found murdered in Littleby's mansion on the rue de Grenelle, and a priceless Indian shawl is missing. Police commissioner "Papa" Gauche recovers only one piece of evidence from the crime scene: a golden key shaped like a whale. Gauche soon deduces that the key is in fact a ticket of passage for the Leviathan, a gigantic steamship soon to depart Southampton on its maiden voyage to Calcutta. The murderer must be among its passengers. In Cairo, the ship is boarded by a young Russian diplomat with a shock of white hair, none other than Erast Fandorin, the celebrated detective of Boris Akunin's The Winter Queen. The sleuth joins forces with Gauche to determine which of ten unticketed passengers on the Leviathan is the rue de Grenelle killer.