He paused, staring at me hard, and: 

“Whoever was watching for your return,” he said solemnly, “mistook Coverly for you!  The moment that Coates drove away, the signal was given.  It must have been.  We were back here a few minutes later, Now do you see?”

“I do not, Gatton!  What are you driving at?”

“At this:  The telephone call must have been made from somewhere in the immediate neighborhood!  There wasn’t time to do it otherwise.  And there is no public call office within a mile which is open after seven o’clock!"

“Good heavens!” I cried.  “At last I understand!”

Gatton looked at me, smiling in grim triumph; and: 

“Dr. Damar Greefe has a residence somewhere within a quarter-mile radius of this house!” he declared.  “He has betrayed himself!  Then—­look here.”

Unscrewing the front of the mouthpiece of the false telephone, he took out the strip of cardboard upon which my number was written, turned it over ... and there upon the back was another number!

“Just look up Dr. Brown-Edwards,” he said.  “He was the last occupant of the Red House, and may still be in the book.”

Grasping the purpose of his inquiry, excitedly I did as he directed; and there sure enough the number appeared!

“The identical instrument that was used at the Red House!” cried Gatton.  “Note the artistic finish with which even the correct exchange numbers are looked up!”

I sank back in my chair, silent, appalled at the perverted genius of this fiend whom we were pitted against in a life-or-death struggle.  But presently: 

“What was the object of the opening and closing of the garage doors at the Red House?” I asked, almost mechanically.

“Simple enough,” Gatton replied.  “Whereas here the telephone was installed, so that the bell could be rung by some one merely calling up your number—­and the ringing stopped by the caller telling the exchange he had made a mistake—­in the Red House, as I have discovered, the ’phone had been disconnected shortly after Dr. Brown-Edwards left the place.”

“Then the opening and closing of the doors was merely a device for ringing the bell?”

“Yes.  The opening of the first door set it ringing and the opening of the second probably stopped it.  Mr. Addison,” he stood up, resting his hands upon the table and regarding me fixedly—­“we enter upon the final battle of wits:  New Scotland Yard versus Dr. Damar Greefe and the green-eyed lady of Bast.  Regarding the latter—­there is a very significant point.”

“What is that?”

“The ‘voice’ on this last occasion was that, not of a woman, but of a man.”

CHAPTER XXIII

THE INEVITABLE

“I very much regret having to trouble you, Miss Merlin, at such a time,” said Inspector Gatton, “but as the paper lodged with you by the late Sir Eric Coverly may throw some light upon a very dark matter, perhaps you will read it to us.”