Paris, 1878 Eccentric antiquarian Lord Littleby and his ten servants are found murdered in Littlebys 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 Akunins 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.
Tipping his hat to Agatha Christie, Akunin assembles a colorful cast of suspects - including a secretive Japanese doctor, a professor who specializes in rare Indian artifacts, a pregnant Swiss woman, and an English aristocrat with an appetite for collecting Asian treasures - all of who are confined together until the crime is solved. As the Leviathan steams toward Calcutta, will Fandorin be able to out-investigate Gauche and discover who the killer is, even as the ships passengers are murdered, one by one?