Sherlock Holmes did not reply to the question, but continued his directions:
“Now, take the letter B. Move it back and forth as you would a bolt.”
Devanne did so, and, to his great surprise, it produced a clicking sound.
“Quite right,” said Holmes. “Now, we will go to the other end of the word Thibermesnil, try the letter I, and see if it will open like a wicket.”
With a certain degree of solemnity, Devanne seized the letter. It opened, but Devanne fell from the ladder, for the entire section of the bookcase, lying between the first and last letters of the words, turned on a pivot and disclosed the subterranean passage.
Sherlock Holmes said, coolly:
“You are not hurt?”
“No, no,” said Devanne, as he rose to his feet, “not hurt, only bewildered. I can’t understand now.... those letters turn.... the secret passage opens....”
“Certainly. Doesn’t that agree exactly with the formula given by Sully? Turn one eye on the bee that shakes, the other eye will lead to God.”
“But Louis the sixteenth?” asked Devanne.