Arsene Lupin 12: The Secret Tomb

Dorothy, a ropedancer and palmist, arrives at the Château de Roborey with her travelling circus, made up of motley crew of war orphans and notices strange excavations at the grounds.
As a long day ends, Dorothy grows worried about her friend Saint-Quentin a young boy with a passion for adventure and a penchant for getting into trouble. Dorothy sets out to hunt for Quentin.
Remembering the castle they had recently discovered, and recalling that it had fascinated Saint-Quentin who had wanted to break in, Dorothy makes her way to a rocky outcrop surrounding the rampart, where she discovers a lurking figure. She quickly hides and observes as he furtively opens up a secret passage into a hidden lair. Just then, she sees Saint-Quentin climb out of a castle window, which the man also sees and aims a rifle at Saint-Quentin, forcing Dorothy to rush out and save Saint-Quentin's life, and is now plunged headlong into mystery and adventure.
The ensuing mystery involves the lord and lady of the Chateau de Roborey, a family secret involving Dorothy herself, a quest for long-lost ancestral treasure and a name from the distant past but Dorothy's new-found nemesis is always close on her trail.
The Secret Tomb was released in 1923. Although Arsène Lupin does not feature in the book, this adventure novel, is set in the world of Lupin (Cagliostro). The main character Dorothée solves one of Lupin's four fabulous secrets and hence The Secret Tomb is considered the twelfth novel in the Arsene Lupin series of books by French author Maurice Leblanc. This yellowback reissues all fourteen of leblanc's Lupin adventures available in English.
Lupin's four fabulous secrets are what he learns from Josephine, the four fabulous secrets of Queen Marie-Antoinette and Cagliostro: 1) ALCOR, or the Seven-Armed Candlestick; 2) The Hollow Needle; 3) The God-Stone of the King of Bohemia; and 4) In Robore Fortuna (La Comtesse de Cagliostro).

Maurice Marie Émile Leblanc was a French novelist and writer of short stories, known primarily as the creator of the gentleman burglar, adventurer and detective Arsène Lupin, often described as a French counterpart to Arthur Conan Doyle's Sherlock Holmes and Hornung's Raffles.
Refusing the career that his father had set up for him at a card factory, Leblanc instead went to Paris in 1888, to pursue writing as a journalist. But he soon turned novelist and storyteller. His first novel, Une femme (A Woman), published in 1893 was a success and was followed by other works, such as Des couples (The Couples), Voici des ailes (Here are wings) and a play La pitié, released in 1902, which was a flop. In 1905, Pierre Lafitte, the director of the monthly Je sais tout, commissioned a short story from Leblanc, with the brief that he was to combine the appeal of A.J Raffles by Ernest William Hornung and Sherlock Holmes. The result was L'Arrestation d'Arsène Lupin (The Arrest of Arsène Lupin) which was a huge success. Two years later, the book Arsène Lupin, Gentleman Burglar was released, and the rest was history—with one of the most successful series being born.