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.
"Well, the police investigated the matter, and, as usual, discovered no clue whatever."
"They never do, when Arsène Lupin is concerned in it."
"Exactly; and so I decided to ask the assistance of Herlock Sholmes, who replied that he was ready and anxious to enter the lists with Arsène Lupin."
"What glory for Arsène Lupin!" said Velmont. "But if our national thief, as they call him, has no evil designs on your castle, Herlock Sholmes will have his trip in vain."
"There are other things that will interest him, such as the discovery of the subterranean passage."
"But you told us that one end of the passage was outside the ramparts and the other was in this very room!"
"Yes, but in what part of the room? The line which represents the passage on the charts ends here, with a small circle marked with the letters `T.G.,' which no doubt stand for `Tour Guillaume.' But the tower is round, and who can tell the exact spot at which the passage touches the tower?"
Devanne lighted a second cigar and poured himself a glass of Benedictine. His guests pressed him with questions and he was pleased to observe the interest that his remarks had created. The he continued:
"The secret is lost. No one knows it. The legend is to the effect that the former lords of the castle transmitted the secret from father to son on their deathbeds, until Geoffroy, the last of the race, was beheaded during the Revolution in his nineteenth year."
"That is over a century ago. Surely, someone has looked for it since that time?"
"Yes, but they failed to find it. After I purchased the castle, I made a diligent search for it, but without success. You must remember that this tower is surrounded by water and connected with the castle only by a bridge; consequently, the passage must be underneath the old moat. The plan that was in the book in the National Library showed a series of stairs with a total of forty-eight steps, which indicates a depth of more than ten meters. You see, the mystery lies within the walls of this room, and yet I dislike to tear them down."
"Is there nothing to show where it is?"
"Nothing."
"Mon. Devanne, we should turn our attention to the two quotations," suggested Father Gélis.
"Oh!" exclaimed Mon. Devanne, laughing, "our worthy father is fond of reading memoirs and delving into the musty archives of the castle. Everything relating to Thibermesnil interests him greatly. But the quotations that he mentions only serve to complicate the mystery. He has read somewhere that two kings of France have known the key to the puzzle."
"Two kings of France! Who were they?"
"Henry the Fourth and Louis the Sixteenth. And the legend runs like this: On the eve of the battle of Arques, Henry the Fourth spent the night in this castle. At eleven o'clock in the evening, Louise de Tancarville, the prettiest woman in Normandy, was brought into the castle through the subterranean passage by Duke Edgard, who, at the same time, informed the king of the secret passage. Afterward, the king confided the secret to his minister Sully, who, in turn, relates the story in his book, "Royales Economies d'Etat," without making any comment upon it, but linking with it this incomprehensible sentence: `Turn one eye on the bee that shakes, the other eye will lead to God!'"
After a brief silence, Velmont laughed and said:
"Certainly, it doesn't throw a dazzling light upon the subject."
"No; but Father Gélis claims that Sully concealed the key to the mystery in this strange sentence in order to keep the secret from the secretaries to whom he dictated his memoirs."
"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 Gèlis, "but I am confident the solution is contained in those two sentences, and some day we will find a man able to interpret them."
"Herlock Sholmes 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."
"What is it?"
"The missing key. Now that I have it, I can go to work at once," said Velmont.
"Of course; without losing a minute," said Devanne, smiling.
"Not even a second!" replied Velmont. "To-night, before the arrival of Herlock Sholmes, I must plunder your castle."
"You have no time to lose. Oh! by the way, I can drive you over this evening."
"To Dieppe?"
"Yes. I am going to meet Monsieur and Madame d'Androl and a young lady of their acquaintance who are to arrive by the midnight train."
Then addressing the officers, Devanne added:
"Gentlemen, I shall expect to see all of you at breakfast to-morrow."
The invitation was accepted. The company dispersed, and a few moments later Devanne and Velmont were speeding toward Dieppe in an automobile. Devanne dropped the artist in front of the Casino, and proceeded to the railway station. At twelve o'clock his friends alighted from the train. A half hour later the automobile was at the entrance to the castle. At one o'clock, after a light supper, they retired. The lights were extinguished, and the castle was enveloped in the darkness and silence of the night.
The moon appeared through a rift in the clouds, and filled the drawing-room with its bright white light. But only for a moment. Then the moon again retired behind its ethereal draperies, and darkness and silence reigned supreme. No sound could be heard, save the monotonous ticking of the clock. It struck two, and then continued its endless repetitions of the seconds. Then, three o'clock.
Suddenly, something clicked, like the opening and closing of a signal-disc that warns the passing train. A thin stream of light flashed to every corner of the room, like an arrow that leaves behind it a trail of light. It shot forth from the central fluting of a column that supported the pediment of the bookcase. It rested for a moment on the panel opposite like a glittering circle of burnished silver, then flashed in all directions like a guilty eye that scrutinizes every shadow. It disappeared for a short time, but burst forth again as a whole section of the bookcase revolved on a picot and disclosed a large opening like a vault.
A man entered, carrying an electric lantern. He was followed by a second man, who carried a coil of rope and various tools. The leader inspected the room, listened a moment, and said:
"Call the others."
Then eight men, stout fellows with resolute faces, entered the room, and immediately commenced to remove the furnishings. Arsène