en Cuevana 3. Jacques d'Athys, a French adventurer, returns to his home in Nice after an expedition to Indochina where he has picked up a Eurasian fiancée and a book that, unbeknownst to him, contains a coded message revealing the whereabouts of both secret treasures and sensitive government intelligence. This makes him the target of foreign spies, including a Marquise of mysterious Latin origin, a Hindu hypnotist and an evil German doctor, who will stop at nothing to obtain the book.