lied. 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
Sherlock Holmes, 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