“You were very curious the other morning, I recall, respecting my object in borrowing a large brace and bit.  My object, Petrie, was to bore a series of holes in the wainscoating of various rooms at the Gables—­in inconspicuous positions, of course . . .”

“But, my dear Smith!” I cried, “you are merely adding to my mystification.”

He stood up and began to pace the room in his restless fashion.

“I had cross-examined Weymouth closely regarding the phenomenon of the bell-ringing, and an exhaustive search of the premises led to the discovery that the house was in such excellent condition that, from ground-floor to attic, there was not a solitary crevice large enough to admit of the passage of a mouse.”

I suppose I must have been staring very foolishly indeed, for Nayland Smith burst into one of his sudden laughs.

“A mouse, I said, Petrie!” he cried.  “With the brace-and-bit I rectified that matter.  I made the holes I have mentioned, and before each set a trap baited with a piece of succulent, toasted cheese.  Just open that grip!”

The light at last was dawning upon my mental darkness, and I pounced upon the grip, which stood upon a chair near the window, and opened it.  A sickly smell of cooked cheese assailed my nostrils.

“Mind your fingers!” cried Smith; “some of them are still set, possibly.”

Out from the grip I began to take mouse-traps!  Two or three of them were still set but in the case of the greater number the catches had slipped.  Nine I took out and placed upon the table, and all were empty.  In the tenth there crouched, panting, its soft furry body dank with perspiration, a little white mouse!

“Only one capture!” cried my companion, “showing how well-fed the creatures were.  Examine his tail!”

But already I had perceived that to which Smith would draw my attention, and the mystery of the “astral bells” was a mystery no longer.  Bound to the little creature’s tail, close to the root, with fine soft wire such as is used for making up bouquets, were three tiny silver bells.  I looked across at my companion in speechless surprise.

“Almost childish, is it not?” he said; “yet by means of this simple device the Gables has been emptied of occupant after occupant.  There was small chance of the trick being detected, for, as I have said, there was absolutely no aperture from roof to basement by means of which one of them could have escaped into the building.”

“Then . . .”

“They were admitted into the wall cavities and the rafters, from some cellar underneath, Petrie, to which, after a brief scamper under the floors and over the ceilings, they instinctively returned for the food they were accustomed to receive, and for which, even had it been possible (which it was not) they had no occasion to forage.”

I, too, stood up; for excitement was growing within me.  I took up the piece of silk from the table.