“Louis the sixteenth was a clever locksmith. I have read a book he wrote about combination locks. It was a good idea on the part of the owner of Thibermesnil to show His Majesty a clever bit of mechanism. As an aid to his memory, the king wrote: 3-4-11, that is to say, the third, fourth and eleventh letters of the word.”
“Exactly. I understand that. It explains how Lupin got out of the room, but it does not explain how he entered. And it is certain he came from the outside.”
Sherlock Holmes lighted his lantern, and stepped into the passage.
“Look! All the mechanism is exposed here, like the works of a clock, and the reverse side of the letters can be reached. Lupin worked the combination from this side—that is all.”
“What proof is there of that?”
“Proof? Why, look at that puddle of oil. Lupin foresaw that the wheels would require oiling.”
“Did he know about the other entrance?”
“As well as I know it,” said Holmes. “Follow me.”
“Into that dark passage?”
“Are you afraid?”