An old knife, a gift from a friend in the Dutch Indies, was driven into the wainscoting, about three feet above the secrétaire and half-way between the floor and the ceiling.
Now, what was that old knife doing there?
A few hours previous to this discovery it was lying safe and snug in Balthazar's desk.
At the same moment Tricamp drew attention to the fact that the wire which was attached to the bell was twisted and broken and was fastened about the handle of the knife. He sprang upon a chair, and from there to the top of the desk, from whence he proceeded to examine this bit of fresh evidence.
Suddenly he gave a cry of triumph. He only had to raise his hand between the knife and the picture molding to ascertain that a large piece of wall paper had been cut out, together with the wood and the plastering, the whole being replaced with a care to defy the closest inspection.
This discovery was so unexpected that the young men could not withhold their admiration at the sergeant's skill. M. Tricamp remarked that the paper had been removed with the greatest skill, thus denoting the work of a professional thief. Raising himself on tiptoe, he placed his hand through the opening and assured himself that the paper in the adjoining room had been tampered with in precisely the same manner.
There was no longer any room for doubt; the thief had certainly entered the room through this aperture. M. Tricamp descended from his pedestal and proceeded to describe the movements of the malefactors from the moment of their arrival until their departure, just as if he had witnessed the whole performance.
"The manner in which that knife has been planted in the wall plainly proves that it was intended as a step to assist the thief in his descent. The wire was used as a sort of rope by which he guided himself on his way back. Now, doesn't this strike you as being rational enough?"
Balthazar and Cornelius listened to this explanation with bated breath. But the former was not the kind of man to enthuse over a description of a theft, especially when he was the loser by the operation. What he wanted to know was where his medallion had gone; now that he knew how the thief had entered, he was anxious to know how he had gone out.
"Have patience," remarked M. Tricamp, following up his clue with professional pride; "now that we know their movements, we must assure ourselves as to their temperament—"