"this is where the mystery centers," said gatton.

i made no reply, for i had not yet recovered from the shock of that discovery in the deserted supper room. it was so wholly unexpected and yet it so cruelly confirmed the inspector's undisguised suspicions that it seemed to me to have created a sort of impalpable barrier between us. of this gatton was evidently conscious. he endeavored to arouse my interest in the inquiries which he was conducting in the garage, but for long enough i saw nothing of the place in which we stood; i could only see that photograph smiling at me inquiringly through a haze of doubt, and my companion's words reached me in a muffled fashion. finally, however, i succeeded in rousing myself from this dazed condition, and confident as ever that isobel was innocent of all complicity in the matter:

"the presence of the photograph," i said, "takes us a step further. don't you see, inspector, that this is a deeply and cunningly laid trap? what i had taken for a series of unfortunate coincidences i perceive now to be the workings of an elaborate scheme involving perfectly innocent people in the crime."

"h'm," said gatton doubtfully; "it may be as you suggest; at any rate it is a new point of view and one which i confess had not occurred to me. there is one witness who can clear up any doubt on the subject."

"you mean marie?"

"exactly. she will lie, beyond doubt, but we shall find means to reach the truth."

"would it not be advisable, inspector," i asked excitedly, "to make sure of her at once?"

gatton smiled grimly, and:

"marie would have to make herself invisible to evade scotland yard now," he replied. "she is being watched closely. but," he continued, "what do you make of these marks on the door?"

we had reclosed the garage door and now were standing immediately inside. the marks to which my companion had drawn my attention were situated high up near the roof.

"this may account for the statement of bolton that the door seemed more difficult to open last night than to-day," he said. "unless i am greatly mistaken, some sort of attachment existed here until quite recently."

"possibly a contrivance for reclosing the door?" i suggested.

the marks in fact roughly corresponded to those which would be made by the presence of such a contrivance and there seemed to have been some attempt where it had been removed to disguise the holes left by the screws.

"but the purpose of it?" muttered gatton helplessly.

"god knows," i said; "the purpose of the whole thing is a mystery beyond me entirely."

"assuming that such a piece of mechanism as you suggest had been attached to the door," mused gatton, "you would have noticed its operation last night, unless one of you held the door open."

"neither of us held the door!" i interrupted excitedly. "i remember that we stood just outside looking in. i was behind the constable and he was directing the rays of his lantern into the place."

"h'm," muttered gatton. "then it wasn't a contrivance for closing the door; it was something else. suppose we investigate the other door?"

we proceeded to the other door and i became aware of an intense curiosity respecting what we should find, and of a conviction too that there would be evidence here of another attachment. in this i was quite correct. some piece of mechanism had evidently been fastened to this door also. together we stood staring up at these tell-tale screw-holes and then rather blankly we stared at one another.

"we only lack one thing," said gatton; "the scheme upon which all these contrivances and apparently isolated episodes were hung together. nothing, as we have already assumed, was accident, and nothing coincidence. it was with some deliberate purpose that the constable was instructed to walk through this garage, opening and shutting the doors behind him."

"from whom did these instructions come?"

"that is one of the minor points which i have already cleared up," he replied. "on my way here i called at the house agent's, as you know, since i have the keys; i also called at the station. the sergeant who was on duty last night i could not see, unfortunately, but i learned—that it was a woman who rang up."

my heart sank lower and lower. it seemed to me as we stood in that empty garage that an invisible hand was drawing a net closer and closer about isobel and my ideas became increasingly chaotic, for the purpose of it all eluded me, try how i would to conceive of a scheme by which any one could profit which necessitated the imprisonment, or worse, of isobel.

"and the agent?" i asked in a rather toneless voice.

gatton shook his head.

"i have no reason to doubt the word of this man of business," he replied, "because at the time when i saw him he could not possibly have learned of the crime, but nevertheless his account is almost unbelievable. it appears then, he, too, received his instructions throughout by telephone."

"what?" i exclaimed.

"by telephone," repeated gatton. "he was rung up about ten days ago by some one who made a verbal offer to lease the red house for a period of twelve months. a foreigner, who in lieu of the usual references, was prepared to pay the annual rent in advance. as the red house, to use an irishism, was regarded as something of a white elephant, the agent was interested, apparently; and when on the following day the sum agreed upon arrived by post, he did not demur about delivering the keys to the prospective lessee, who desired to take certain measurements in regard to carpets and so forth."

"wait a moment," i interrupted; "to whom did he deliver these keys?"

"to a district messenger who called for them, as the agent had been advised that one would do."

"very well. what then?"

"that is all that the agent had to say."

"what, that is all?"

"substantially there is nothing more. it is quite evident that the sole intention of this unknown lessee was to secure possession of the house for the purpose of the crime only."

"do you mean that from first to last no one but the district messenger appeared in the matter?"

"no one," gatton assured me, "and the rent, payment of which quite disarmed the agent of course, was sent in the form of treasury notes and not by check."

"but surely some name, some address, must have been given?"

"a name was given," replied gatton, "and a hotel address, but confirmation of their accuracy was never sought, after the receipt of the money."

"and the voice on the telephone?"

again i saw that odd expression creep over gatton's face, and:

"it was a woman's voice," he answered.

"great heavens!" i muttered—"what does it all mean?"

that the evidence of the cabman when he was discovered and of the carter who had taken the box from the garage to the docks, and (for it was possibly the same man) who had first delivered it at the red house, would but tighten the net about isobel, whom i knew to be innocent, i felt assured.

"gatton," i said, "this case appears to me to resolve itself into a deliberate conspiracy of which the end was not the assassination of sir marcus, but the conviction of miss merlin!"

gatton looked at me with evident complexity written all over him.

"i begin to think the same," he confessed. "this business was never planned and carried out by a woman, i'll swear to that. there is a woman concerned in it, for at every point we come upon evidence of her voice issuing the mysterious instructions; but she is not alone in the matter. already the intricacy of the thing points to a criminal of genius. when we know the whole truth, if we ever do, that the crime was planned by a man of amazing, if perverted, intellect, will be put beyond dispute, i think."

"what is puzzling me, gatton," i said, "is the connection existing between the incidents which took place in this garage and those, unknown at present, which took place in the furnished room in the red house."

"obviously," replied gatton, "a supper for two had been prepared, and that one of those two was the late sir marcus is perfectly obvious. that he expected the other to be miss merlin is at least suggested by the presence of her photograph in the room; for you will have noticed that it is the only photograph there."

"nevertheless," i said firmly, "i am positive that no one would be more surprised than herself to learn of its presence."

"and as i have already said," replied gatton, "i am rapidly coming round to your way of thinking. but even if i were quite sure of it the evidence at the moment is all the other way, you will admit. as to the connection between this garage and the interrupted supper party (for obviously it was interrupted) this it must be my business to find out."

"don't you think," i said, "that we are attaching perhaps undue importance to the fact that some kind of fittings have been removed from the doors? they may have been removed by the late occupier, and the call to the police depot may have been made with the idea of securing a witness, and a credible one, to the presence of the crate here on the night of the murder."

"at the moment," replied gatton, musingly, "i cannot see that this would have served any useful purpose; but nevertheless you may be right. i am going to assume, however, that you are wrong, and that the object of sending bolton here last night was to open and shut these doors. i propose now to return again to the scene of the interrupted supper."

leaving the garage not very much wiser than when we had entered it, we paced once more up the drive in the shade of the big trees and were greeted again by the malarious smell of rotting leaves. entering the red house, gatton and i proceeded first to that incredible oasis in the desert of empty rooms and my companion made a detailed examination of everything in the place, even sounding the walls, examining the fittings of the door, and finally proceeding through the hall in the direction of the south wing of the house—that nearest to the garage.

what he expected to find i had no idea, but his attention seemed to be more particularly directed towards the wainscot and the picture-rails of the empty and uncarpeted rooms which we entered. whatever he had sought he failed to find, and at last we stood in a desolate apartment looking out into the tangled shrubbery before the windows. the back of the garage was visible from there and i viewed it dully, wondering what evil secret it held, and marveling at the trick of fate which had made me witness of an act in this gruesome drama.

"of course, gatton," i said, "we are all along assuming that sir marcus actually met his death in this house. we must remember that he may merely have been brought here after the crime."

"such a short period elapsed," replied the inspector, "between his leaving the new avenue theater and the approximate time of his death that it seems unlikely that he visited any intermediate spot."

"but he may not have been in the crate when bolton and i saw it."

"i don't believe he was in the crate then," replied gatton, "but i think he was at the red house nevertheless."

i stared at him with curiosity.

"you mean that he was in the house at the time that the constable and i opened the garage?"

"i do. i think he was in that room where supper was laid for two."

"good god!" i exclaimed; for there was something horrible in the idea of the man who now lay murdered having been in the house presumably alive, whilst bolton and i had stood within forty yards of him; in the idea that it had lain in our power, except for those human limitations which rendered us ignorant of his presence, to have averted his fate, perhaps to have checked the remorseless movement of this elaborate murder machine which seemingly had been set up in the red house.

"some one was here last night," declared gatton suddenly, as we turned to leave the deserted room, "after you and bolton had gone. everything incriminating the assassin has been removed. looking at the matter judicially, it becomes quite evident that any one clever enough to have planned this crime could not possibly have been guilty of an act of such glaring stupidity as that of accidentally leaving a photograph planted upon the mantelpiece."

that this fact had presented itself to the inspector with such a force of conviction raised a great load from my mind. it had all along been evident to me, but i had feared that to the official outlook of my companion, and the official outlook is always peculiar, it might have seemed otherwise.

"the clever and cunning villain who planned this thing," i said, "has overstepped himself, as you say, gatton. if the murder was planned artistically, in his attempt to throw the onus of the crime upon innocent shoulders he has been guilty of a piece of very mediocre work. it would not deceive a child."

"no, i agree with you there. the discovery of that photograph has done more to convince me of the innocence of miss merlin than any amount of testimonials to her good character could ever have done. you see," he added, smiling whimsically, "all sorts of people hitherto unsuspected by their closest friends of criminal tendency, develop that taint, so that i am never surprised to find a convicted thief or assassin possessed of credentials which would do justice to an archbishop. but when i see an obviously artificial clew i recognize it a mile off. real clews never stare you in the face like that."

coming out of the front door, we walked down the leaf-strewn drive to find that the constable on duty at the gate had been joined by a plain-clothes man who was evidently waiting to speak to the inspector.

"yes?" said gatton eagerly, at sight of the newcomer.

"we have her, sir," he reported tersely.

"does he refer to marie?" i asked.

gatton nodded.

"i think, mr. addison," he said, "i will proceed immediately to bow street, where she has been taken to be interrogated. will you come with me or are you otherwise engaged?"

i hesitated ere i replied:

"i do not particularly want to confront this woman, but i should be much indebted if you could let me know the result of your examination."

"i shall do that without fail," said gatton, "and some time to-day i should be obliged if you could provide me with the facts concerning the little cat-images which you said you had in your possession."

"certainly," i agreed. "you are still of the opinion that the mark upon the crate and the image of the cat-woman have an important bearing upon the crime?"

"i don't doubt it," was the reply. "if the photograph clew is a false one, the cat clew is a true one and one to be followed up. perhaps," he added, "it would be as well if you returned now and looked out the points which you think would be of interest, as when i come i may not have long to stay."

"i will do so," i said, "although i think i can lay my hands upon the material almost immediately."

accordingly gatton set off with the detective who had brought the news of marie's arrest and i, turning in the opposite direction, proceeded towards my cottage in such a state of mental tumult respecting what the end of all this would be and what it might mean for isobel, that i found myself unable to think connectedly; and needless to say i failed to conjure up by any stretch of the imagination a theory which could cover this amazing and terrible sequence of events.