"Good Gad, man!" exclaimed Verplanck, who had read it over Craig's shoulder. "What do you make of THAT?"

Kennedy merely shook his head. Mrs. Verplanck was the calmest of all.

"The light," I cried. "You remember the light? Could it have been a signal to some one on this side of the bay, a signal light in the woods?"

"Possibly," commented Kennedy absently, adding, "Robbery with this fellow seems to be an art as carefully strategized as a promoter's plan or a merchant's trade campaign. I think I'll run over this morning and see if there is any trace of anything on the Carter estate."

Just then the telephone rang insistently. It was McNeill, much excited, though he had not heard of the orange incident. Verplanck answered the call.

"Have you heard the news?" asked McNeill. "They report this morning that that fellow must have turned up last night at Belle Aire."

"Belle Aire? Why, man, that's fifty miles away and on the other side of the island. He was here last night," and Verplanck related briefly the find of the morning. "No boat could get around the island in that time and as for a car—those roads are almost impossible at night."

"Can't help it," returned McNeill doggedly. "The Halstead estate out at
Belle Aire was robbed last night. It's spooky all right."

"Tell McNeill I want to see him—will meet him in the village directly," cut in Craig before Verplanck had finished.

We bolted a hasty breakfast and in one of Verplanck's cars hurried to meet McNeill.

"What do you intend doing?" he asked helplessly, as Kennedy finished his recital of the queer doings of the night before.

"I'm going out now to look around the Carter place. Can you come along?"

"Surely," agreed McNeill, climbing into the car. "You know him?"

"No."

"Then I'll introduce you. Queer chap, Carter. He's a lawyer, although I don't think he has much practice, except managing his mother's estate."

McNeill settled back in the luxurious car with an exclamation of satisfaction.

"What do you think of Verplanck?" he asked.

"He seems to me to be a very public-spirited man," answered Kennedy discreetly.

That, however, was not what McNeill meant and he ignored it. And so for the next ten minutes we were entertained with a little retail scandal of Westport and Bluffwood, including a tale that seemed to have gained currency that Verplanck and Mrs. Hollingsworth were too friendly to please Mrs. Verplanck. I set the whole thing down to the hostility and jealousy of the towns people who misinterpret everything possible in the smart set, although I could not help recalling how quickly she had spoken when we had visited the Hollingsworth house in the Streamline the day before.

Montgomery Carter happened to be at home and, at least openly, interposed no objection to our going about the grounds.

"You see," explained Kennedy, watching the effect of his words as if to note whether Carter himself had noticed anything unusual the night before, "we saw a light moving over here last night. To tell the truth, I half expected you would have a story to add to ours, of a second visit."

Carter smiled. "No objection at all. I'm simply nonplussed at the nerve of this fellow, coming back again. I guess you've heard what a narrow squeak he had with me. You're welcome to go anywhere, just so long as you don't disturb my study down there in the boathouse. I use that because it overlooks the bay—just the place to study over knotty legal problems."

Back of, or in front of the Carter house, according as you fancied it faced the bay or not, was the boathouse, built by Carter's father, who had been a great yachtsman in his day and commodore of the club. His son had not gone in much for water sports and had converted the corner underneath a sort of observation tower into a sort of country law office.

"There has always seemed to me to be something strange about that boathouse since the old man died," remarked McNeill in a half whisper as we left Carter. "He always keeps it locked and never lets anyone go in there, although they say he has it fitted beautifully with hundreds of volumes of law books, too."

Kennedy had been climbing the hill back of the house and now paused to look about. Below was the Carter garage.

"By the way," exclaimed McNeill, as if he had at last hit on a great discovery, "Carter has a new chauffeur, a fellow named Wickham. I just saw him driving down to the village. He's a chap that it might pay us to watch—a newcomer, smart as a steel trap, they say, but not much of a talker."

"Suppose you take that job—watch him," encouraged Kennedy. "We can't know too much about strangers here, McNeill."

"That's right," agreed the detective. "I'll follow him back to the village and get a line on him."

"Don't be easily discouraged," added Kennedy, as McNeill started down the hill to the garage. "If he is a fox he'll try to throw you off the trail. Hang on."

"What was that for?" I asked as the detective disappeared. "Did you want to get rid of him?"

"Partly," replied Craig, descending slowly, after a long survey of the surrounding country.

We had reached the garage, deserted now except for our own car.

"I'd like to investigate that tower," remarked Kennedy with a keen look at me, "if it could be done without seeming to violate Mr. Carter's hospitality."

"Well," I observed, my eye catching a ladder beside the garage, "there's a ladder. We can do no more than try."

He walked over to the automobile, took a little package out, slipped it into his pocket, and a few minutes later we had set the ladder up against the side of the boathouse farthest away from the house. It was the work of only a moment for Kennedy to scale it and prowl across the roof to the tower, while I stood guard at the foot.

"No one has been up there recently," he panted breathlessly as he rejoined me. "There isn't a sign."

We took the ladder quietly back to the garage, then Kennedy led the way down the shore to a sort of little summerhouse cut off from the boathouse and garage by the trees, though over the top of a hedge one could still see the boathouse tower.

We sat down, and Craig filled his lungs with the good salt air, sweeping his eye about the blue and green panorama as though this were a holiday and not a mystery case.

"Walter," he said at length, "I wish you'd take the car and go around to Verplanck's. I don't think you can see the tower through the trees, but I should like to be sure."

I found that it could not be seen, though I tried all over the place and got myself disliked by the gardener and suspected by a watchman with a dog.

It could not have been from the tower of the boathouse that we had seen the light, and I hurried back to Craig to tell him so. But when I returned, I found that he was impatiently pacing the little rustic summerhouse, no longer interested in what he had sent me to find out.

"What has happened?" I asked eagerly.

"Just come out here and I'll show you something," he replied, leaving the summerhouse and approaching the boathouse from the other side of the hedge, on the beach, so that the house itself cut us off from observation from Carter's.

"I fixed a lens on the top of that tower when I was up there," he explained, pointing up at it. "It must be about fifty feet high. From there, you see, it throws a reflection down to this mirror. I did it because through a skylight in the tower I could read whatever was written by anyone sitting at Carter's desk in the corner under it."

"Read?" I repeated, mystified.

"Yes, by invisible light," he continued. "This invisible light business, you know, is pretty well understood by this time. I was only repeating what was suggested once by Professor Wood of Johns Hopkins. Practically all sources of light, you understand, give out more or less ultraviolet light, which plays no part in vision whatever. The human eye is sensitive to but few of the light rays that reach it, and if our eyes were constituted just the least bit differently we should have an entirely different set of images.

"But by the use of various devices we can, as it were, translate these ultraviolet rays into terms of what the human eye can see. In order to do it, all the visible light rays which show us the thing as we see it—the tree green, the sky blue—must be cut off. So in taking an ultraviolet photograph a screen must be used which will be opaque to these visible rays and yet will let the ultraviolet rays through to form the image. That gave Professor Wood a lot of trouble. Glass won't do, for glass cuts off the ultraviolet rays entirely. Quartz is a very good medium, but it does not cut off all the visible light. In fact there is only one thing that will do the work, and that is metallic silver."

I could not fathom what he was driving at, but the fascination of
Kennedy himself was quite sufficient.

"Silver," he went on, "is all right if the objects can be illuminated by an electric spark or some other source rich in the rays. But it isn't entirely satisfactory when sunlight is concerned, for various reasons that I need not bore you with. Professor Wood has worked out a process of depositing nickel on glass. That's it up there," he concluded, wheeling a lower reflector about until it caught the image of the afternoon sun thrown from the lens on the top of the tower.

"You see," he resumed, "that upper lens is concave so that it enlarges tremendously. I can do some wonderful tricks with that."

I had been lighting a cigarette and held a box of safety wind matches in my hand.

"Give me that matchbox," he asked.

He placed it at the foot of the tower. Then he went off, I should say, without exaggeration, a hundred feet.

The lettering on the matchbox could be seen in the silvered mirror, enlarged to such a point that the letters were plainly visible!

"Think of the possibilities in that," he added excitedly. "I saw them at once. You can read what some one is writing at a desk a hundred, perhaps two hundred feet away."

"Yes," I cried, more interested in the practical aspects of it than in the mechanics and optics. "What have you found?"

"Some one came into the boathouse while you were away," he said. "He had a note. It read, 'Those new detectives are watching everything. We must have the evidence. You must get those letters to-night, without fail.'"

"Letters—evidence," I repeated. "Who wrote it? Who received it?"

"I couldn't see over the hedge who had entered the boathouse, and by the time I got around here he was gone."

"Was it Wickham—or intended for Wickham?" I asked.

Kennedy shrugged his shoulders.

"We'll gain nothing by staying here," he said. "There is just one possibility in the case, and I can guard against that only by returning to Verplanck's and getting some of that stuff I brought up here with me. Let us go."

Late in the afternoon though it was, after our return, Kennedy insisted on hurrying from Verplanck's to the Yacht Club up the bay. It was a large building, extending out into the water on made land, from which ran a long, substantial dock. He had stopped long enough only to ask Verplanck to lend him the services of his best mechanician, a Frenchman named Armand.

On the end of the yacht club dock Kennedy and Armand set up a large affair which looked like a mortar. I watched curiously, dividing my attention between them and the splendid view of the harbor which the end of the dock commanded on all sides.

"What is this?" I asked finally. "Fireworks?"

"A rocket mortar of light weight," explained Kennedy, then dropped into
French as he explained to Armand the manipulation of the thing.

There was a searchlight near by on the dock.

"You can use that?" queried Kennedy.

"Oh, yes. Mr. Verplanck, he is vice-commodore of the club. Oh, yes, I can use that. Why, Monsieur?"

Kennedy had uncovered a round brass case. It did not seem to amount to much, as compared to some of the complicated apparatus he had used. In it was a four-sided prism of glass—I should have said, cut off the corner of a huge glass cube.

He handed it to us.

"Look in it," he said.

It certainly was about the most curious piece of crystal gazing I had ever done. Turn the thing any way I pleased and I could see my face in it, just as in an ordinary mirror.

"What do you call it?" Armand asked, much interested.

"A triple mirror," replied Kennedy, and again, half in English and half in French, neither of which I could follow, he explained the use of the mirror to the mechanician.

We were returning up the dock, leaving Armand with instructions to be at the club at dusk, when we met McNeill, tired and disgusted.

"What luck?" asked Kennedy.

"Nothing," he returned. "I had a 'short' shadow and a 'long' shadow at Wickham's heels all day. You know what I mean. Instead of one man, two—the second sleuthing in the other's tracks. If he escaped Number One, Number Two would take it up, and I was ready to move up into Number Two's place. They kept him in sight about all the time. Not a fact. But then, of course, we don't know what he was doing before we took up tailing him. Say," he added, "I have just got word from an agency with which I correspond in New York that it is reported that a yeggman named 'Australia Mac,' a very daring and clever chap, has been attempting to dispose of some of the goods which we know have been stolen through one of the worst 'fences' in New York."

"Is that all?" asked Craig, with the mention of Australia Mac showing the first real interest yet in anything that McNeill had done since we met him the night before.

"All so far. I wired for more details immediately."

"Do you know anything about this Australia Mac?"

"Not much. No one does. He's a new man, it seems, to the police here."

"Be here at eight o'clock, McNeill," said Craig, as we left the club for Verplanck's. "If you can find out more about this yeggman, so much the better."

"Have you made any progress?" asked Verplanck as we entered the estate a few minutes later.

"Yes," returned Craig, telling only enough to whet his interest.
"There's a clue, as I half expected, from New York, too. But we are so
far away that we'll have to stick to my original plan. You can trust
Armand?"

"Absolutely."

"Then we shall transfer our activity to the Yacht Club to-night," was all that Kennedy vouchsafed.