i was about half-way on my return journey when i heard a car racing along the road behind me, and as it came nearer i detected the fact that it was slowing down. ere i could turn:

"hi! mr. addison!" hailed a voice.

i stopped, turned round, and there was gatton leaning out of the car and staring towards me through the deepening dusk.

"why, gatton!" i said, walking up to him—"i waited more than ten minutes for you, and then gave it up."

"waited for me?"

"yes, by the police-box."

he stared in evident wonder at me and then at the police chauffeur who drove the car.

"whatever prompted you to do that?" he said. "coates must have given you the wrong message. i said i would come to the house for you, not meet you in the street."

still i remained dense to the truth, and:

"i know you did," i replied. "i refer to the second message."

"i sent no second message."

"what!"

"get in," cried gatton shortly; "this wants explaining."

i stepped into the car, and as it moved onward again i explained to the inspector what had taken place. as i talked i saw his expression grow darker and darker, until finally:

"there's something wrong!" he muttered.

"then you did not inspire the message?"

"i know nothing whatever about it. at the time you received it i was on my way from crossleys. i have been traveling for the last hour and a half."

i stared at him very blankly. the object of such a communication was difficult to imagine, and i knew of nothing incriminating in my possession, which might have tempted the assassin to lure me from the house whilst he obtained possession of it.

in ever-growing excitement i watched the houses slipping behind us as we swept along. then we came to the tree-lined expanse of road immediately leading to the cottage. as the car stopped, i leaped out quickly, gatton close upon my heels, and ran up the path to the door.

from certain indications with which i was familiar, i observed that coates was out, whereby i concluded that he had set off to meet the mythical "man with a box." not without apprehension i inserted the key in the lock and opened the door.

as i did so, i beheld a most singular spectacle.

the careful coates had closed all the windows as usual before quitting the house, so that there was comparatively little draught along the corridor. but as the door swung open i perceived a sort of gray fog-like vapor floating over the carpet about a foot in depth and moving in slightly sinuous spirals upward towards the opened door!

at this phenomenon i stared in speechless astonishment; for whilst it resembled steam or the early morning mist which one sometimes sees upon the grass in hot weather, i was wholly at a loss to account for its presence inside my cottage!

"good heavens!" cried gatton, and grasped me by the arm with so strong a grip that i almost cried out. "look! look!"

"what the devil is it?" i muttered; and turning, i stared into his face. "what can it be?"

"stand back," he said strangely, and pulled me out into the porch. "do you notice a peculiar smell?"

"i do—a most foul and abominable smell."

gatton nodded grimly.

"god knows what has happened here since you left," he said; "but of one thing i am sure—you must certainly bear a charmed life, mr. addison. there has been a third attempt at your removal!"

this choking smell which now rose to my nostrils had in it something vaguely familiar, yet something which at that place and that time i found myself unable to identify; but:

"we shall have to open the windows!" rapped gatton.

suiting the action to the word, he took out his handkerchief, and holding it to his nostrils went running along the corridor, his feet oddly enveloped in that mysterious mist. a moment later i heard the bang of a swiftly raised window, then another, and:

"stand clear of the door!" called a muffled voice.

a moment later gatton came racing back again, coughing and choking because of the fumes which arose from that supernatural fog carpeting the passages.

the chauffeur now appeared upon the path leading from the gate to the porch, but:

"stay by the car!" ordered gatton. "don't move without instructions."

i scarcely noted his words. for i was watching the gray fog. in the dusk i could see it streaming out, that deathly mist, and creeping away across grass and flower-beds, right and left of the door.

"give it a chance to clear," said gatton; "i fancy one good whiff would finish any man!"

even as he spoke the words the nature of this vapor suddenly occurred to me, and:

"the abbey inn!" i whispered. "the abbey inn!"

"ah!" said he—"you've solved the mystery, have you? but can you explain how this stuff comes to be floating about the floor of your house?"

"i cannot," i confessed. "but at all costs we must go in. we must learn the worst!"

"yes, we'll risk it now," said the inspector.

close together we entered and made our way towards the study. as we passed the door-way of the ante-room in which the telephone was placed. i glanced, aside, and thereupon:

"my god, gatton!" i groaned. "look!"

he pulled up and the two of us stood, horror-stricken, rooted to the spot, looking into the little room.

i have said that coates invariably closed the windows before leaving the house, but here the window was open. prone upon the floor was stretched the figure of a man!

he wore a light overcoat, and his hat lay under the telephone table—where it had evidently rolled at the moment of his fall. the poisonous smell was more apparent here than elsewhere; and looking down at the prone figure, the face of which was indiscernible because of the man's position:

"why, gatton!" i said in an awed whisper—"look!... he was speaking to some one!"

"i'm looking!" replied gatton grimly.

grasped rigidly in his left hand the fallen man held the telephone!

"we want gas-masks for this job," said the inspector.

his words were true enough. i had already recognized the odor of the foul stuff. it was identical with that which, as we had come down from the upper floor of the abbey inn, had proceeded from the room wherein the mysterious shell had exploded. in a word my cottage was filled with some kind of poison-gas!

"we must risk it, anyway," said gatton, "and find out who it is."

i nodded, sick with foreboding. stooping swiftly, he succeeded in turning over the prone figure, whereupon i quite failed to restrain a hoarse cry of horror....

it was eric coverly!

the fume-laden room seemed to swim around me as i looked down at the dreadfully contorted features over which was creeping that greenish tint which had characterized the face of sir marcus as i had seen it on the morning of the body's recovery from the hold of the oritoga.

"drag him out," said gatton huskily; "he may be alive."

but even as we bent to the attempt, both my companion and i were seized with violent nausea; for the wisps of gray mist which still floated in the air were nevertheless sufficiently deadly. however, we succeeded at last in dragging eric coverly into the passage. here it became necessary to detach the telephone from the death-grip in which he held it.

i turned my head aside whilst gatton accomplished this task; then together we bore coverly out into the porch. at this point we were both overcome again by the fumes. gatton was the first to recover sufficiently to stoop and examine the victim of this fiendish outrage. i clutched dizzily at an upright of the porch, and:

"don't tell me he's dead," i whispered.

but gatton stood up and nodded sternly.

"he was the last!" he said strangely. "they have triumphed after all."

the man who had driven the car and who now stood in a state of evident stupefaction looking over the gate, where he had been warned to remain by the inspector, came forward on seeing gatton beckoning to him.

"notify the local officer in charge and bring a doctor," said gatton. he turned to me. "which is the nearest?"

rapidly i gave the man the necessary instructions and he went running out to the car and soon was speeding away towards the house of a local physician.

i find it difficult to recapture the peculiar horror of the next few minutes, during which, half-fearful of entering the cottage, gatton and i stood in the little sheltered garden adjoining the porch looking down at the body of this man who had met his end under my roof, in circumstances at once dreadful and incomprehensible.

tragically, eric coverly was vindicated; by his death he was proved innocent. and by the manner of his death we realized that he had fallen a victim to the same malign agency as his cousin.

i have explained that my cottage stood in a strangely secluded spot, although so near to the sleepless life of london; and i remember that throughout the period between the departure of the man with the car and his return with the doctor and two police officers whom he had brought from the local depot, only one pedestrian passed my door and he on the opposite side of the road.

how little that chance traveler suspected what a scene was concealed from his eyes by the tall hedges which divided the garden from the highroad! it was as the footsteps of this wayfarer became faint in the distance, that suddenly:

"come along!" said gatton. "we might chance it now. i want to get to the bottom of this telephone trick."

we returned to the door of the ante-room, and side by side stood looking down at the telephone which had only been extracted from the grip of the dead man with so much difficulty. the inspector stooped and took it up from the floor. the deadly gray mist was all but dissipated now, and together we stood staring stupidly at the telephone which gatton held in his hand.

to all outward seeming 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 from," i said, as gatton and i walked through the cottage to meet the new arrivals.

"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 pass 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 anticipated. 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 substitution 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 brass-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 assassin 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 assassin!"

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 bâst. 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."