“Has he sent you a warning, as he did to Baron Cahorn?”
“No,” replied Devanne, “he can’t work the same trick twice.”
“What then?”
“I will show you.”
He rose, and pointing to a small empty space between the two enormous folios on one of the shelves of the bookcase, he said:
“There used to be a book there—a book of the sixteenth century entitled ‘Chronique de Thibermesnil,’ which contained the history of the castle since its construction by Duke Rollo on the site of a former feudal fortress. There were three engraved plates in the book; one of which was a general view of the whole estate; another, the plan of the buildings; and the third—I call your attention to it, particularly—the third was the sketch of a subterranean passage, an entrance to which is outside the first line of ramparts, while the other end of the passage is here, in this very room. Well, that book disappeared a month ago.”
“The deuce!” said Velmont, “that looks bad. But it doesn’t seem to be a sufficient reason for sending for Sherlock Holmes.”
“Certainly, that was not sufficient in itself, but another incident happened that gives the disappearance of the book a special significance. There was another copy of this book in the National Library at Paris, and the two books differed in certain details relating to the subterranean passage; for instance, each of them contained drawings and annotations, not printed, but written in ink and more or less effaced. I knew those facts, and I knew that the exact location of the passage could be determined only by a comparison of the two books. Now, the day after my book disappeared, the book was called for in the National Library by a reader who carried it away, and no one knows how the theft was effected.”
The guests uttered many exclamations of surprise.
“Certainly, the affair looks serious,” said one.