As I entered the laboratory I saw before him a peculiar, telescope-like instrument, at one end of which, in a jar of oxygen, something was burning with a brilliant, penetrating flame.

He paused in his work and I hastened to tell him of the peculiar experience I had had in the forenoon. But he said nothing, even at the significant actions of Dr. Preston.

"How about those things you found in the maid's room?" I asked at length. "Do they explain Rawaruska's death?"

"The trouble with them," he replied, thoughtfully shaking his head, "is that the effects of such things last only for a short time. They might have been used at first—but there was something used afterward."

"Something afterward?" I repeated, keenly interested, and fingering the telescope-like arrangement curiously. "What's this?"

"One of the new quartz lens spectroscopes used by Dr. Dobbie of the English Government laboratories," he answered briefly. "I think chemists, police officials, coroners and physicians are going to find it most valuable. You see, by throwing the ultra-violet part of the spectrum from a source of light as I obtain from the sparking of iron in oxygen through the lenses of a quartz spectroscope, the lines of many dangerous drugs, especially of the alkaloids, can be distinctly and quickly located in the spectrum. Each drug produces a characteristic kind of line. We use a quartz lens because glass cuts off the ultra-violet rays. Why, even the most minute particle of poison can be detected in this revolutionary fashion."

He had resumed squinting through the spectroscope.

"Well," I asked, "do you find anything there?"

He had evidently been using the piece of gauze on which he had preserved the liquid from the peculiar little marks on Rawaruska's spine.

"Narcophin," he muttered, still squinting.

"Narcophin?" I repeated. "What is that?"

"A derivative of opium—morphine. There's another poison here, too," he added.

"What is it?"

"Scopolamine," he answered tersely, "scopolamine hydrobromide."

"Why," I exclaimed, "that is the drug they use in this new 'twilight sleep,' as they call it."

"Exactly," he replied, "the dÄmmerschlaf. I suspected something of the kind when I saw those little punctures on her back. Some people show a marked susceptibility to it; others just the reverse. Evidently she was one of those who go under it quietly and quickly."

I looked at Kennedy in amazement.

"You can see," he went on, catching the expression on my face, "if it could be used for medical science, it could also be used for crime. That's the way I reasoned, the way someone else must have reasoned."

He paused, then went on. "Someone thought out this plan of using narcophin and scopolamine to cause the twilight sleep, to keep Rawaruska just on the borderland of unconsciousness, destroying her memory and producing forgetfulness. That is the dÄmmerschlaf; perception is retained but memory lost. You are acquainted with the test? They show an object to a patient and ask her if she sees it. Say, half an hour later, it is shown again. If she remembers it, it is a sign that a new injection is necessary.

"Only in this case the criminal went too far, disregarded the danger of the thing. Scopolamine in too great a quantity causes death by paralysis of respiration—a paralysis, by the way, against which artificial respiration and all means of stimulating are ineffective because of the rigidity of the muscles. And so, you see, in this case Rawaruska died."

I could not help thinking of Preston, the young doctor who had been studying in Germany. More than likely he had heard of and had investigated the Frieberg "twilight sleep" treatment. We had made some progress, even though we did not know why or by whom the drugs had been administered.

Wade, of the Customs Service, had, as I have said, told us that he had several secret agents about in the trade, constantly picking up bits of information that might interest the Treasury Department. It did not surprise Kennedy, therefore, late in the forenoon, to have Wade call up and tell him that among the early callers at Margot's, the jeweler, was the maid Cecilie.

"That was where she must have been before I reached the Vanderveer," I exclaimed.

Kennedy nodded. "But why did she go there?" he asked. "And why was she talking with Preston?"

Inasmuch as I couldn't answer the questions I didn't try, but waited while Craig reasoned out some method of attack on them.

"Since it's known that we're working on the case of Rawaruska," he ruminated half an hour later over an untasted lunch, "we might just as well take the risk of seeing Margot himself. Let's go down and look his shop over."

So in the middle of the afternoon, when Fifth Avenue was crowded with shoppers, we paused before Margot's window, looking over the entrancing display of precious stones gleaming out from the rich black velvet background, and then sauntered in, like any other customers.

Kennedy engaged the salesman in talk about necklaces and lavallieres, always leading the conversation around to the largest stones that he saw, and dwelling particularly on those that were colored. As I listened, trying to throw in a word now and then that would not sound absolutely foolish, I was impressed by a feeling that Margot's, even though it was such a fashionable place, was what might be called only a high-class shyster's. In fact, I recalled having heard that Margot had engineered several rather questionable transactions in gems.

"I'm much interested in orange stones," remarked Kennedy, casually turning up a flawless white diamond and discarding it as if it did not interest him. "Once when I was abroad I saw the famous Invincible, and a handsomer gem than it is I never hope to see."

The clerk, ever obliging, replaced the tray before us in the safe and retired toward the back of the shop.

"He suspects nothing, at least," whispered Kennedy.

A moment later he returned. "I'm sorry," he reported, "but we haven't any such stones in the house. But I believe we expect some in a few days. If you could—"

"I shall remember it; thank you," interrupted Kennedy brusquely, as I caught a momentary gleam of satisfaction in his eye. "That's most fortunate. I'll be in again. Thank you."

We turned toward the door. In an instant it flashed over me that perhaps they were recutting the big Invincible.

"Just a moment, please, gentlemen," interrupted a voice behind us.

A short, stocky man had come up behind us.

"I thought you did not look like purchasers, nor yet like crooks," he said defiantly. "Did I hear you refer to the Invincible?"

It was Margot himself, who had been hovering about behind us. Kennedy said nothing.

"Yes," he went on, "I am cutting a large diamond, but it is not like the Invincible. It is much handsomer—one that was discovered right here in this country in the new diamond fields of Arkansas. The diamond itself is already sold. And you would nevair guess the buyer, oh, nevair!"

"No?" queried Kennedy.

"Nevair!" reiterated Margot.

"It could not be delivered to a woman who was once the maid of Rawaruska, the Russian dancer?" Craig asked abruptly.

Margot shot a quick and suspicious glance at us.

"Then you are, as I suspected, a detectif?" he cried.

Kennedy eyed him sharply without admitting the heinous charge. Margot returned his look and I felt that of all sayings that about a dishonest man not being able to look you in the eye was itself the least credible. He laughed daringly. "Well, perhaps you are right," he said. "But whoever it is, he is lucky to have bought a stone like it so cheaply!"

The man was baffling. I could not figure it out. Had Margot been simply a high-class "fence" for the disposal and convenient reappearance of stolen goods?

We returned uptown to our apartment to find that in the meantime Wade had called up again. Kennedy got him on the wire. It seemed that shortly after we left Margot's Cecilie had called again and had gone off with a small, carefully wrapped package.

"A strange case," pondered Kennedy, as he hung up the receiver. "First there is a murder that looks like a suicide, then the sale of a diamond that looks like a fake." He paused a moment. "They have worked quickly to cover it up; we must work with equal quickness if we are to uncover them."

With almost lightning rapidity he had seized the telephone again and had our old friend First Deputy O'Connor on the wire. Briefly he explained the case, and arranged for the necessary arrests that would bring the principal actors in the little drama to the laboratory that night. Then he fell to work on a little delicate electrical instrument consisting, outwardly at least, of a dial with a pointer and several little carbon handles attached to wires, as well as a switchboard.

I know that Kennedy did not relish having his hand forced in this manner, but nevertheless he was equal to the emergency and when, after dinner, those whom O'Connor had rounded up began to appear at the laboratory, no one would ever have imagined that he had not the entire case on the very tip of his tongue, almost bursting forth an accusation.

De Guerre had complied with the police order by sending Cecilie alone in a cab, and later he drove up with Miss Hoffman. Dr. Preston came in shortly afterward, shooting a keen glance at Cecilie, and avoiding more than a nod to De Guerre. Margot himself was the last to arrive, protesting volubly. Wade, of course, was already there.

"I really must beg your pardon," began Kennedy, as he ignored the querulousness of Margot, the late arrival, adding significantly, "that is, of all of you except one, for monopolizing the evening."

Whatever might have been in their minds to say, no one ventured a word. Kennedy's tone when he said, "Of all of you except one," was too tense and serious. It demanded attention, and he got it.

"I am going to put to you first a hypothetical case," he continued quietly. "Let us say that the De Guerres of Antwerp decided to smuggle a great jewel into America for safe keeping, perhaps for sale, during the troublous times in their own country.

"Now, any man would know," he went on, "that he had a pretty slim chance when it came to smuggling in a diamond. Besides, everyone knew that the De Guerres owned this particular stone, of which I shall speak later. But a woman? Smuggling is second nature to some women."

Quickly he ran over the strange facts that had been unearthed regarding the death of the dainty Russian dancer.

"You were right, Monsieur De Guerre," he concluded, turning to the diamond merchant; "it was no suicide. Your wife was killed—unintentionally, it is true,—but killed in an attempt to steal a great diamond from her while she was smuggling it."

De Guerre made no answer, save a hasty glance at Wade that did not carry with it an admission of smuggling.

"You mean to say, then, Mr. Kennedy," Margot demanded, "that while Rawaruska was smuggling in the big diamond of which you speak someone heard of it and deliberately murdered her?"

"Not too fast," cautioned Craig. "Think again before you use those words, 'deliberately murdered.' If it had been murder that was intended, how much more surely it might have been accomplished by more brutal methods—or by more scientific. No, murder was never deliberately intended."

He stopped, as if to emphasize the point, then slowly began to distribute to each of us one of the carbon handles I had seen him adjusting to the peculiar little electrical instrument.

"Let me reconstruct the case," he hurried on, giving a final twist or two to the instrument itself, now placed before him on a table, with its dial face away from us. "Rawaruska had retired for the night. Where had she placed the diamond? It would probably take a long search to find it. Well, the twilight sleep was chosen because it was supposed to be a safe and sure means to the end. Even if she retained some degree of consciousness, she would forget what happened. That is partly the reason for the treatment, anyhow,—the loss of memory.

"Someone believed this was a safe and sure anesthetic. First perhaps a whiff of the secret service 'bad perfume' to insure that she would not cry out—then an injection of narcophin and scopolamine—another—and the twilight sleep. A few minutes, and Rawaruska was unconscious.

"Then came the search. Perhaps she was restless. Another injection settled that. At last the great diamond was found. But the twilight sleep meant not forgetfulness but death to Rawaruska!"

Craig paused. It was almost as if one could see the word picture of the scene as he painted it.

"What was to be done? The diamond must be recut—anything to hide its identity, at once, and at any cost. And Margot? The story of the Arkansas diamond and the sale is a blind. The case is perfect!"

Kennedy raised his eyes for the first time from the study of the little electrical machine before him, and caught the eye of Cecilie, holding it, unwilling.

"Did you ever hear of the great diamond, the Invincible?" Kennedy smashed out.

I felt that it might not have been exactly chivalrous, but it was necessary.

Cecilie's breast, which had showed a wildly beating heart as Kennedy told of how her mistress had died, was calmer now. Her air of surprise at the mention of the diamond was perfect. Elsa Hoffman was gazing at her, too, in tense interest. De Guerre was outwardly cool, Margot openly cynical, Preston leaning forward in ill-suppressed excitement.

For a moment Kennedy paused again, as if allowing all to collect themselves before he took them by assault.

"I have lately been studying," he remarked casually, "the experiments of Dr. Von Pfungen of Vienna showing the protective resistance of the human skin against an electric current. Normally, this resistance averages from seventy to eighty thousand ohms. In the morning, owing to the accumulation of waste products, the resistance may mount to almost double. In persons suffering from nervous anxiety, it decreases to five thousand and even down to a thousand ohms in cases of hysteria. Von Pfungen has also measured a human being's emotional feelings by the electric current. I have a copy of his instrument here. There is one person who sits gripping the carbon electric handle connected with this galvanometer who, to begin with, had a resistance of over sixty thousand. But when I began to tell of how Rawaruska met her death, of the hypothetical case I have built up by my observations and experiments here in this very laboratory, the needle of the galvanometer started to oscillate downward. It went down until it reached thirty-eight thousand at the mention of murder. When I said the case was perfect, it had got as low as under twenty thousand, swinging lower and lower as the person saw hope depart!"

Kennedy was no longer paying any attention to the little instrument. As I followed him, I became more and more impatient. What was it he had discovered? Who was it?

"Preston," cried Kennedy, suddenly wheeling on the young doctor, "through your regard—honorable, I am sure—for Rawaruska you have let yourself be drawn into doing a little amateur detective work. Let me warn you. Instead of clearing up the case, you merely laid yourself open to suspicion. Fortunately the galvanometer absolves you. You should have known that Cecilie was only a tool. De Guerre, your black wallet, that all diamond dealers carry—thank you, Wade—that's it."

Kennedy had turned from Preston to Cecilie, then to De Guerre so suddenly that no one was prepared for the signal he gave to the customs officer.

Wade had covered the surprised dealer and was now emptying out the contents of the wallet.

There, on the table, gleaming in the light of the laboratory, lay a wonderful brilliant, some three hundred carats—perfect in its blazing crystalline orange beauty. There it lay, a jewel which might charm and arouse the cupidity of two hemispheres. It shone like a thing of life. Yet back of its orange fire lay a black tragedy.

Margot was on his feet instantly.

"That is not the—"

"Just a moment, Mr. Margot," interrupted Kennedy. "I think Mr. Wade will be able to show that it is the Invincible when he matches up the parts that have been hurriedly cut from—from the wonderful Arkansas diamond," Craig added sarcastically. "Miss Hoffman, Dr. Preston tells us that before you were a diamond saleswoman you had been a trained nurse!"

The look Elsa Hoffman flashed, as her calm exterior refused to conceal her emotions longer, was venomous.

Kennedy was the calmest one of us all as he tapped the little galvanometer significantly with his index finger.

"De Guerre," he exclaimed, leaning forward slightly, "you and your lover, Elsa Hoffman, planned cunningly to rob your own brothers. But, instead of robbers merely," he ground out, "you are murderers!"