In this third instalment of Erast's adventures, he doesn't have a prominent voice. That's not surprising considering none of the chapters are from his point of view. After the murder of an entire household along with it's owner, a collector named Littleby, the only clue left behind is a golden pin for premium members set to board the Leviathan, a luxury cruise liner. Immediately, the French inspector Gauche takes the opportunity to come aboard and investigate the few suspects who all have no choice but to stay. Among them, is a new diplomat on his way to Japan by the name of Erast Fandorin. With his developing deductive powers, he tries to solve the mystery before time runs out and the key to one of the greatest collections of jewels is lost.