"We know more than that," he retorted. "We know how _Sir Marcus_ died!"

"Gatton!" I cried excitedly, as we approached a group waiting in the porch--"do you mean--"

He looked at me grimly.

"I mean," he said slowly, "that I have not forgotten the _gas-plug_ in the wall of that recess in the supper-room at the Red House! The only thing I was doubtful about (the means by which the victim was induced to admit the gas into the room) is now as clear as daylight."

"You are right, Gatton," I agreed. "The same trick has succeeded twice."

"The same trick, as you say, Mr. Addison; with one trifling variation, a device which would only suggest itself to such a brain as that of--"

"Dr. Damar Greefe!" I cried.

"I believe you are right."

And now fell an awesome silence; for whilst Gatton and I stood bare-headed, the unfortunate Eric Coverly was being carried out to the waiting car; and even as I turned my eyes away in horror from that spectacle, I was endeavoring to frame the words in which I should acquaint Isobel with this second ghastly tragedy.

Here, indeed, was a new development of "the _Oritoga_ mystery"; and so queerly does the mind depart from the actualities at such a moment that I found myself thinking, even whilst Gatton was talking to me, of the bold head-lines which would greet readers of the press in the morning--and of the renewed excitement which would sweep throughout the length and breadth of the land when this dreadful alibi was proven.

Over the details of that gruesome tragedy I feel myself compelled to pa.s.s lightly, for even now the horror of it remains with me. The fumes of the poisonous gray mist lingered for hours in the house; and there were official visitations, testimonies and attestations, and the hundred and one formalities which invariably accompany such a tragedy but which I need not deal with in detail here.

Coates returned with the Rover, just as the body of the victim was being removed, and his account of what had occurred was simple enough, and followed the lines which we had antic.i.p.ated. He had locked up and then gone to the garage for the car as I had directed him to do, returning to the cottage in time to admit Eric Coverly, whom he showed into the study, having informed him that I should be back in less than ten minutes. He had then proceeded to Denmark Hill railway station only to find, as I had found, that the appointment was a hoax and "the man with a box" a myth.

"You see," said Gatton, "the scheme of the plotter was simply this: to get Coates out of the way for a long enough time to allow the subst.i.tution of the telephone to be accomplished. The fact that Coates had closed the windows before leaving the house didn't interfere very much with the scheme. It's an old-fashioned catch on the ante-room window, and I have seen the marks upon the bra.s.s-work where it was forced from the outside with the blade of a knife. For the person who opened the window to take out the real telephone and put the other in its place was easy; and all that remained was to lift the gas-cylinder on to the shed and partly reclose the window as we found it. Coates, even if he had troubled to look, would not have noticed any difference in the dusk. It is the next move, however, which _I_ find most interesting."

Gatton spoke with repressed excitement, and:

"What do you mean by 'the next move'?" I asked.

"Well," he replied, "we have good evidence to show that the a.s.sa.s.sin possesses an almost Napoleonic capacity for working by the time-table.

Witness the employment of Constable Bolton in the Red House affair--which showed that our man was perfectly acquainted with the movements of the officer on that beat and timed his scheme accordingly. Very well ... having laid the telephone trap in your ante-room--did our man hurry away and make the call _in person_, which brought Coverly to the 'phone?--or did he remain watching the house and give the signal to _some one else_ to do it?"

"I cannot imagine, Gatton. Nor does the point strike me as important."

"No?" said Gatton, smiling triumphantly. "Then I must explain.

Whereas, in the Red House, the scheme worked _automatically_--for the time of Sir Marcus's arrival was _fixed_--in the present instance, some one had to watch for _your_ return from the mythical appointment!"

"For _my_ return?"

"Unquestionably! This scheme was arranged for your benefit, Mr.

Addison. Unknowingly, poor Coverly saved you from a dreadful fate at the price of his own life! You see, they did not know that Coverly was coming here! Now, it will not have escaped your attention that he wore a soft felt hat, a light overcoat, and carried a black cane. So did _you_ when you went out to keep the appointment made by the a.s.sa.s.sin!"

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."

Uns.c.r.e.w.i.n.g 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."

I watched the play of expression upon Isobel's face with a depth of sympathy which I cannot attempt to describe. The successive trials which had been imposed upon her in so short a time had robbed her cheeks of their sweet color and there were dark shadows under her eyes. The tumult of my own feelings was such that I was scarcely capable of consistent thought nor had I the moral courage to examine those emotions which stirred so wildly within me.

Late on the previous night I had performed the unhappy duty of breaking to her the news of Coverly's dreadful death. I shall never forget that black hour. Her courage, however, under all these trials had been admirable, and although I well knew what it must have cost her, she replied now with perfect composure:

"Look--I took it out of my bureau when I heard that you were here, Inspector."

She took up from the table a foolscap envelope sealed and having her name written upon it in large and somewhat unsteady characters.