The young Archduke Joseph Anton Salvator of Austria has disappeared along with his double. An eight-year-old boy doing odd jobs is found dead at the foot of a hill near Loch Rannoch in Scotland. The deputy director of Huperman & Company, which manufactures the best safes, is trampled by horses on a London street. And two of the most beautiful girls of Dolly Marigold go missing. The same happens to the Great Blue, a raw diamond from the De Beers house, weighing five thousand carats.

Sherlock Holmes, along with Doctor Watson, will be forced to abandon their comfortable life at 221B Baker Street. Thieves, diamond smugglers, American tycoons, broke aristocrats, the governments of three major empires, and the rich and charming Countess D' Espinó, all entangled in the hunt for a priceless trophy: the tiara of the Habsburgs.

[Excerpt from the text on the back cover of the edition]