“That is an ingenious theory,” said Velmont.
“Yes, and it may be nothing more; I cannot see that it throws any light on the mysterious riddle.”
“And was it also to receive the visit of a lady that Louis the Sixteenth caused the passage to be opened?”
“I don’t know,” said Mon. Devanne. “All I can say is that the king stopped here one night in 1784, and that the famous Iron Casket found in the Louvre contained a paper bearing these words in the king’s own writing: ‘Thibermesnil 3-4-11.’”
Horace Velmont laughed heartily, and exclaimed:
“At last! And now that we have the magic key, where is the man who can fit it to the invisible lock?”
“Laugh as much as you please, monsieur,” said Father Gélis, “but I am confident the solution is contained in those two sentences, and some day we will find a man able to interpret them.”
“Sherlock Holmes is the man,” said Mon. Devanne, “unless Arsène Lupin gets ahead of him. What is your opinion, Velmont?”
Velmont arose, placed his hand on Devanne’s shoulder, and declared:
“I think that the information furnished by your book and the book of the National Library was deficient in a very important detail which you have now supplied. I thank you for it.”