“There’s no doubt about it,” I remarked as soon as we had partially recovered from our surprise. “That’s Fuller right enough.”

“Oh! there’s no doubt it’s our man,” said Dennis emphatically. “Even if we had not the evidence of the torn page to corroborate it, the likeness is perfect.”

“Yes,” I agreed, “but what do you think his game can be? I’m coming round to Garnesk’s wireless theory.”

“Whatever it is, we’ve stumbled on something of real importance this time. We must find out what it is and show it up at once.”

“I hope you’ll take care,” said Myra anxiously. “I shouldn’t mind so much if I could be with you to help, but it’s dreadful to sit here and know you are in danger and not be able to do anything at all.”

“I’m very glad you can’t, darling,” I said heartily, as I threw my arm round her shoulders. “I don’t want you to come rushing into these dangers, whatever they may be. In a way I am glad you are not able to join us, because I know how difficult it would be to stop you if you were.”

“I suppose this is all one affair,” she said doubtfully. “You don’t think this is something quite different from the green ray? It might be two quite separate things, you know.”

“I don’t think we are likely to meet with two such interesting problems in such a remote locality unless they are connected with each other, Miss McLeod, and especially as everything else apart from the photograph of Baron von Guernstein points to Fuller as the culprit. I think we can take it that in solving one mystery we provide the solution to the other.”

“I quite agree with you, Dennis,” I said, “but what I am worrying about now is, what we are going to do.”

“The first thing you must do is to dress for dinner, and not let anyone imagine there is anything untoward about,” Myra advised. “And please don’t tell father you have been lunching with one of the Kaiser’s principal spies, if that’s what the Baron’s title really means. I would much rather you said nothing to him at all about it for the present, and in any case you must have something definite in mind as to your plans before you put the matter to him. If you tell him you don’t know what to do about it he will be in a dreadful state. He is very far from well, and all this business has told on him dreadfully.”

“That is very excellent advice, Miss McLeod,” Dennis agreed warmly. “Ronald, we’ll go and disguise ourselves as ordinary, undisturbed human beings and hide our fears and doubts behind the breastplate of a starched shirt. Come along.”

So Dennis dragged me away, and then, realising his indiscretion, allowed me to return to my fiancÉe “just for two minutes, old fellow.”

Dinner was a curious meal, though not quite so strange as the meal the General and I had together the night, less than a week before, that Myra lost her sight.

I hope I shall never live through a week like that again. Even now, as I look back, I cannot believe that it all happened in seven days. It still seems to have been something like seven months at the very least.

We had one thing in our favour as we sat down to the table; we all had a common object in view. We were each of us determined to forget the green ray for a moment. Fortunately the old man took an immediate fancy to Dennis and that brightened me considerably. There are few things so pleasant as to see those whose opinion you value getting on with your friends. Only once, and that after Mary McNiven had come to take poor Myra away, did the subject of the green ray crop up.

“Mr. Burnham knows about it all, I suppose?” the General asked.

“I’ve told him everything, and Garnesk and I went over the whole thing with him before the train went.”

“Good!” said the old man emphatically. “Excellent fellow Garnesk—excellent; in fact, I don’t know when I’ve met such a thundering good chap. No new developments, I suppose?”

I hesitated. I could not have brought myself to lie to him, and in view of the startling complications with which we had so recently been confronted, I was at a loss for an answer. Dennis came to my rescue just in time.

“I think Ron’s difficulty is in defining the word ‘developments,’ General,” said he. “If we said there were developments it would naturally convey the impression that we had something definite to report. I think perhaps the best way to put it would be that we believe we are getting on the right scent, by the simple process of putting two and two together and making them four. We hope to have something very decided to tell you in a day or two.”

“I shall be glad to hear something, I can assure you,” said the old man, “but in the meantime we will try to forget about it. You have had a tiring journey, Mr. Burnham, followed by a strange initiation into what is probably a new sphere of life altogether—the sphere of mysteries and detectives, and so forth. No, Ronald, we’ll give Mr. Burnham a rest for to-night.”

But just as I was congratulating myself that we had escaped from the painful necessity of putting him off with an evasive answer, if not a deliberate lie, the butler entered and announced that he had shown Mr. Hilderman into the library.

“Well, as we are ready, we had better join him,” said the old man, and we adjourned to the other room.

Now if Hilderman should by any tactless remark betray our strange experience in the afternoon there would be the devil to pay. I followed the General into the library, beckoning to the American with a warning finger on my lip. He saw at once what I meant, fortunately, and held his tongue, and we all talked of general matters for some little time. Then Hilderman took the bull by the horns.

“As a matter of fact, General,” he announced boldly, “I ran over to have a word with Mr. Ewart about a certain matter which is interesting us all. I don’t suppose you wish me to worry you with details at the moment?”

“I should be very glad to hear what you have to tell us, Mr. Hilderman, but unfortunately I—er—I have a few letters I simply must write, so I hope you will excuse me. My daughter is in the drawing-room, so perhaps you fellows would care to join her there. Her counsel will be of more use to you than mine in your deliberations, I have no doubt.”

However, when we looked for her in the drawing-room Myra was not there, and I found her in her den.

“Why not bring him in here?” she asked. “He won’t bite, and it will be more conducive to a free and easy discussion. I should like to hear what he has to say for himself in view of his running away this afternoon, and I shouldn’t feel comfortable in the drawing-room with this shade on. In here I feel that he must just put up with any curiosities he meets.”

So we made ourselves comfortable in the den, and Hilderman sat in a chair by the window.

“Of course, you know what I have come to speak about, Mr. Ewart,” he began at once. “You must have thought my conduct this afternoon was very strange—very unsportsmanlike, to say the least.”

“Oh, I don’t know,” I replied as lightly as I could. “It was a very strange affair, and it rather called for strange conduct of one sort or another.”

“Still, you must have thought it cowardly to run away as quickly as I could,” he insisted.

“It was some time before we even noticed you had left us,” I laughed, “and then, I confess, I couldn’t quite make out where you had got to or why you had gone.”

“As a matter of fact we were rather scared,” Dennis put in. “We searched for you in the river.”

“It sounds a very cowardly confession to make,” Hilderman admitted, “but I went back to the landing-stage, got into my boat, and cleared off as quickly as I could. I must ask you to believe that I was under the impression that it would be best for us all that I should. But my idea proved to be a bad one and nothing came of it. So here I am to ask you if you have learned anything or have anything to suggest.”

“I’m afraid we’re more at a loss than ever now,” I admitted. “The further we get with this thing the less we seem to know about it, unfortunately.”

Hilderman was exceedingly sympathetic, and though he made numerous suggestions he was as puzzled as we were ourselves. I had some difficulty in defining his attitude. We knew as much as was sufficient to hang his friend “Fuller,” but I could not make up my mind whether he really was a friend of von Guernstein’s or not. It was a small thing that decided me. On an occasionable table beside the American lay a steel paper-knife, a Japanese affair, with a carved handle and a very sharp blade. Hilderman picked up the knife and toyed with it.

“I should be careful with that, Mr. Hilderman,” I advised. “That is a wolf in sheep’s clothing; it’s exceedingly sharp.”

“Oh, yes!” cried Myra. “If you mean my paper-knife, it ought not really to be used as a paper-knife at all, the point is like a needle. I must put it away or hang it up as an ornament.”

The American laughed and laid the knife down again on the table, and we resumed our discussion. Both Dennis and I knew that we must be very careful to conceal our suspicions, but at the same time we did our best to reach some sort of conclusion with regard to Hilderman himself.

“And, I suppose, until you have searched about the Saddle,” he remarked, “you will be no further on as to who stole Miss McLeod’s dog. It seems to me that the dog was taken by the man who wished to conceal an illicit still, and the green flash, or green ray, or whatever you call it, is simply a manifestation of some strange electrical combination in the air.”

“I’m afraid we shall have to leave it at that,” I said with an elaborate sigh of regret.

“Not when you have Mr. Burnham’s distinguished powers of deduction to assist you, surely, Mr. Ewart?” said Hilderman, and waited for an answer.

“Flukes are not very consistent things, I fear,” Dennis supplied him readily, “and if we are to make any progress we shall hardly have time for idle speculation.”

“Fortune might continue to favour you,” the American persisted. “Don’t you think it’s worth trying?”

“I’m afraid not,” said Dennis, with a laugh that added emphasis and conviction to his statement.

“By the way,” Myra suggested, “I don’t know if anybody would care for a whisky and soda or anything. I won’t have drinks served in here, but if anybody would like one, you know where everything is, Ron. I always say if anyone wants a drink in my den they can go and get it, and then I know they really like being in the den. You see I’m a woman, Mr. Hilderman,” she laughed.

“I must say I think the idea of refreshment would not enter the head of anyone who had the pleasure of your company here, Miss McLeod, unless you suggested it yourself.”

We laughed at the rather heavy compliment, and I went into the dining-room to fetch the decanters, syphons and glasses.

“I’ll help you to get them,” called Dennis, and followed me out of the room.

“Well?” I asked as soon as we reached the other room. “What do you make of it?”

“I’m not sure,” Dennis admitted. “I’m puzzled. I shouldn’t be surprised if he turned out to be a Government secret service man keeping an eye on Fuller-von-Guernstein, and that when he has quite made up his mind that the mystery of the green ray is connected with his own business he will show his hand.”

“Something of the same sort occurred to Garnesk,” I said. “Well, at present we’d better avoid suspicion and go back before he thinks we’re holding a committee meeting.”

So I led the way to the den. I was walking carefully and slowly, because I was unaccustomed to carrying trays of glasses and things, and consequently I made no noise. I pushed the door open with my shoulder, Dennis following with a couple of syphons, and as I did so I chanced to glance upwards.

In a large mirror which hung over the fireplace I saw the reflection of Hilderman’s face, knitted in a fierce frown, gazing intently at some object which was outside my view. Myra was talking, though what she was saying I did not notice. I went into the room and put the tray on the big table, and as I filled the glasses I looked round casually to see what Hilderman had been looking at. Lying on the sofa on which Myra was sitting was the copy of the Pictures, open at the page bearing the incriminating photograph!

I mixed Hilderman’s drink according to his instructions—for by this time he had entirely recovered his equanimity—and handed it to him. As I did so I happened to look in the direction of the small table beside him. Myra’s Japanese paper-knife was still there, but the point had been stuck more than an inch into the mahogany top of the table. I turned away quickly, with a laughing remark to Myra, which did not seem to raise any suspicion at the time, though I have no recollection now what it was I said.

A few moments afterwards I quietly and unostentatiously slipped out of the room. Surely there could be no doubt about it now. The whole thing was obvious. Hilderman had noticed the paper, jumped to the conclusion that we suspected everything, and in the sudden access of baffled rage had picked up the paper-knife and stabbed it into the table.

There was only one possible reason for that—Hilderman was an enemy. In that case, I thought, he has come here to try and find out how much we know and to keep an eye on us. Possibly he might be attempting to keep us there so that Fuller could get up to some satanic trick elsewhere. I decided to act at once. I turned back to the den and put my head round the door.

“Will you people excuse me for a bit?” I said lightly. “The General wants me.” And with that I left them. I had almost asked Hilderman not to go till I came back, but I was afraid it might sound suspicious to his acute ears. I hardly knew what to do. I should have liked to have been able to speak with Dennis, if only for a moment. Indeed, I am quite ready to confess that just then I would have given all I possessed for ten minutes’ conversation with my friend. I stole quietly out of the house, and thought furiously.

If Hilderman wanted to keep us from spying on Fuller, where was Fuller? Would I be wiser to wait and try to keep an eye on Hilderman, or was my best plan to ignore him and try and locate his German friend? I decided on the latter course. I went back and wrote a short note to Dennis and slipped it inside his cap.

“I’m convinced they are both enemies. Take care of Myra. I may be out all night. Don’t let her worry about me; I may not be back for some time, but I shall come back all right.—R.”

I left this for my friend, knowing that sooner or later he would find it, and went down to the landing-stage. The Baltimore II. and Myra’s boat, the Jenny Spinner, were drawn up alongside, and I realised that if I took the Jenny I should be raising Hilderman’s suspicions at once. Anchored a little way out was another small motor-boat—the first the General had—which Myra had also called after a trout fly—the Coch-a-Bondhu—though the play upon words was lost on most people. The boat was still in constant use, and Angus and Hamish continually went into Mallaig and Glenelg in it to collect parcels and so on. I ran to the petrol shed, and got three tins of Shell, put them in the dinghy and pushed out to the Bondhu, climbed on board, sounded the tank, filled it up, and started out across the Loch. I can only plead my anxiety to get well out of sight and hearing before Hilderman should think of leaving the house, as an excuse for my lamentable thoughtlessness on this occasion. Indeed, it was not till long afterwards that I realised I had forgotten to anchor the dinghy, and I left it, just as it was, to drift out to sea on the tide.

I made all the pace I could and reached the other side in about twenty minutes. I was sadly equipped for an adventurous expedition! I had no flask to sustain me in case of need, no weapon in case I should be called to defend myself; I was wearing a dinner-jacket, no hat, and a pair of thin patent-leather pumps!

I ran the boat right in shore, heedless of the danger to the propeller, in a small sandy cove round the point, so that I was hidden from Glasnabinnie. Then I realised that I had been a little too precipitate in my departure. There was no anchor-chain on board, and the painter was admirably suited for making fast to pier-heads and landing-stages at high tide, but was nothing like long enough to enable me to make the craft secure on short. However, I dragged her as far up as I could, and prayed that I might be able to return before the tide caught her up and carried her away. In those circumstances I should have been stranded in the enemy’s country, by no means a pleasing prospect!

Having done the best I could for Myra’s faithful motor-boat, I made my way round the hill, climbing cautiously upwards all the time, my dinner-jacket carefully buttoned in case a gleam of moonlight on my shirt-front should give me away at a critical moment. It was a rocky and difficult climb, and I soon regretted that I had not taken the bridle path to Glasnabinnie and made my way boldly up the bed of the burn. However, it was too late to turn back, and eventually, after one or two false steps and stumbles, I succeeded in reaching a spot from which I could obtain a good view of the hut. No, there was no light there, no sign of movement at all. I decided to work my way round to the other side and then, if I continued to get no satisfaction, to descend to the house. The windows of the hut, or smoking-room, as the reader will no doubt remember, extended the whole length of the structure; and surely, I thought, if there were a light in the place it would be bound to be visible. I edged round the face of a steep crag, floundered across the stream between the two falls, getting myself soaked above the knees as I did so, and crouched among the heather on the other side of the building. No, there was no one there, the place was deserted. I knelt down and peered about me listening intently.

Not a sound greeted my expectant ear save the incessant rumble of the falls. Then as I turned my attention to the house itself and looked down the course of the burn to Glasnabinnie, I could scarcely suppress a cry of astonishment. For there below me, moving to and fro between the house and the hut, was a constant procession of small lights, like a slowly moving stream of glow-worms, twenty or thirty yards apart. I was rooted to the spot. What could it mean? Was this another weird natural manifestation, or was it, as was much more likely, a couple of dozen men bearing lights? Yes, that was it, men bearing lights—and what else besides? Men don’t climb up and down steep watercourses in the night for the sake of giving an impromptu firework display to an unexpected visitor, I told myself. There was only one thing to do, and that was to investigate the matter and chance what might happen to me. I crept down to the hut, and lay on my face among the heather and listened. Here and there a mumble of voices, now and then a subdued shout, apparently an order to be carried out by the mysterious light-bearers, broken occasionally by the shrill call of a gull, conveyed nothing to me that I could not see. I looked up at the hut. No, there was no one there, and the windows were not screened, because I could see the moonlight streaming through the far side. Yet, surely, the hut must be their objective, I thought. Where else could they be going to? Fascinated, I crawled on my hands and knees till I could touch the walls of the smoking-room by putting out my arm. I heard a great commotion coming, it seemed, from the very ground beneath my feet.

I laid my ear to the ground and listened. The noise grew louder, and the voices seemed to be shouting against a more powerful sound—the waterfall, possibly. I thought perhaps the floor of the hut would give me more opportunity to locate the source of the disturbance. I threw caution to the winds and slipped through the wide windows into the room. I moved as carefully as I could, however, once my feet found the floor, for if there should be anyone below they would probably hear me up above. I turned back the carpet in order to hear more distinctly, and as I did so I noticed a rectangular shaft of light which trickled through the floor. There was a trap-door. I knelt down and lifted it cautiously by a leather tab which was attached to one side of it and peered through. I can never understand how it was I did not drop that hatch again with a self-confessing crash when I realised the extraordinary nature of the sight that greeted my eyes. There was I in the smoking-hut of a peaceful American citizen, where only a few hours before I had spent a pleasant hour in friendly conversation, and now I was lying on the edge of the entrance to a great cavern.

Below me there was a confused mass of machinery and men. Some were working on scaffolding, others were many feet below. The nearest of them was so close to me that I could have leaned down and laid my hand on his head. I tried to make out what they were doing, but except that they were dismantling the machinery, whatever it might be, I could make nothing of it. I watched them breathlessly, trembling lest at any moment one of them should look up and detect my presence.

The place was lighted by electricity, though there were not enough lamps to illuminate the cavern very brightly, and as my eyes got accustomed to the lights and shadows I was able to make out the cause of this.

Evidently there was a turbine engine below, driven by the water from the falls, which supplied the necessary power. After a moment or two it dawned on me how the cavern came to be there; it was, or had been, the course of a hidden river, such as are common enough among the mountains, but the stream had been diverted, probably by some sort of landslide, and had left this tumbler-shaped cave, resembling a pit shaft. Now, I thought, I have only to find out what all this machinery is for and the whole mystery is solved. I opened the trap a little further, and allowed my body to hang slightly over the edge.

Then for the first time I saw, to my right, fixed so that it almost touched the floor of the hut, a great round brass object, mounted on an enormous tripod, which, again, stood on a platform. In front of this was a large square thing like a mammoth rectangular condenser, such as is used for photographic enlarging and other projection purposes. Had it not been for this condenser I should have taken the whole thing to be an elaborate searchlight. But, I asked myself, what would be the good of a searchlight there? Suddenly the whole truth dawned upon me.

The searchlight must operate through a trap in the wall of the hut just below the floor. I leaned further in, forgetting my danger in the intoxication of sudden discovery.

Only a foot or two away from me a man was working on the searchlight. Carefully taking it to pieces, he was handing the parts to another man, who was perched on the scaffold below him. He was so close to me that I could hear him breathing. I was about to wriggle back to safety when he looked up. He gave a sudden loud shout. I lay there fascinated. After all, I thought, before they can reach me I can slip out and edge round the cliff, run down on to the shore, and get away in the motor-boat. But I had reckoned without my host. Even as the man shouted, and the others left their work to see what was the matter, Fuller dashed out from behind the platform, gave one terrified look at me, and, flinging himself at the wall of the cavern, threw all his weight on a rope which dangled there. I scuttled to my feet, intending to make a bolt for it. But the boards shivered beneath me, and, before I could realise what was happening, I found myself hurtling through the air to the floor of the cavern below.