1. The first enigma was solved by a young girl (see The Secret Tomb, by Maurice Leblanc). The two next were solved by Arsène Lupin (see The Island of the Thirty Shrouds and The Hollow Needle). The solving of the fourth is the theme of this book.

  2. Hitherto none of the biographies of Josephine have given any explanation of the fact that she in a way fled from Fontainebleau. Only Monsieur Frederic Masson, scenting the truth, writes: “Perhaps one day some letter will be found which will demonstrate the physical necessity of this departure.”

  3. There is no doubt that the well-known legend of the Thousand Millions of the Congregations had its origin in this tithe.

  4. The acquisition of the treasure of the Kings of France, the second enigma of Cagliostro, and the discovery of that impenetrable retreat from which, fifteen years later, he could only be dislodged by the help of a flotilla of torpedo-boats, dates from this epoch.