ming it was an ordinary instrument, and my number
was written upon it in the space provided for the purpose. Then, all
at once, as we stepped into the room, I observed something out of the
ordinary.

I could see a length of green cable proceeding from the wall-plug
_out_ through the open window. The cable attached to the instrument
which Gatton held did not come from the proper connection at all, but
came _in_ through the window, and was evidently connected with
something outside in the garden!

"What does this mean, Gatton?" I cried.

Evidently as deeply mystified as I, Gatton placed the telephone on the
little table and fully opening the window, leaned out.

"Hullo!" he cried. "The cable leads up to the roof of the tool-shed!"

"To the roof of the tool-shed!" I echoed incredulously.

But Gatton did not heed my words, for:

"What the devil have we here?" he continued.

He was hauling something up from the flower-bed below the window, and
now, turning to me, he held out ... a second telephone!

"Why, Gatton!" I cried, and took it from his hand, "_this_ is the
authentic instrument! See! It is connected in the proper way!"

"I see quite clearly," he replied. "It was simply placed outside,
whilst a duplicate one was substituted for it. I observe a ladder
against the shed. Let us trace the cable attached to the duplicate."

The ladder was one used by Coates about the garden; and now, climbing
out of the window, Gatton mounted it and surveyed the roof of the
lean-to which I used as a tool-shed.

"Ha!" he exclaimed. "A gas cylinder!"

"What!"

He fingered the green cable.

"This is not cable at all," he cried; "it's _covered tubing_! Do you
see?"

He descended and rejoined me.

"You see?" he continued. "A call from the exchange would ring the bell
in the ante-room here. This devilish contrivance"--he pointed to the
false telephone--"is really hollow. The weight of the receiver
hermetically closes the end of the tube, no doubt. But any one
answering the call and taking up the duplicate instrument would
receive the full benefit of the contents of the cylinder which lies
up there on the roof!"

"My God, Gatton!" I muttered. "The fiends! But why was the contrivance
not removed?"

"They hadn't time," he said grimly. "They had not counted on the
death-grip of the victim!"

I heard a car come racing up to the gate, followed by the sound of
many excited voices.

"At last we know where the gray mist came f