It was only after a few hours that Kennedy thought it wise to try to question the poor girl at the hospital. Her story was simple enough in itself, but it certainly complicated matters considerably without throwing much light on the case. She had been busy because her day was full, and she had yet to dress the hair of Miss Blaisdell for her play that night. Several times she had been interrupted by impatient messages from the actress in her little dressing-booth, and one of the girls had already demolished the previous hair-dressing in order to save time. Once Agnes had run down for a few seconds to reassure her that she would be through in time.

She had found the actress reading a newspaper, and when Kennedy questioned her she remembered seeing a note lying on the dresser. "Agnes," Miss Blaisdell had said, "will you go into the writing-room and bring me some paper, a pen, and ink? I don't want to go in there this way. There's a dear good girl." Agnes had gone, though it was decidedly no part of her duty as one of the highest paid employes of the Novella. But they all envied the popular actress, and were ready to do anything for her. The next thing she remembered was finishing the coiffure she was working on and going to Miss Blaisdell. There lay the beautiful actress. The light in the corridor had not been lighted yet, and it was dark. Her lips and mouth seemed literally to shine. Agnes called her, but she did not move; she touched her, but she was cold. Then she screamed and fled. That was the last she remembered.

"The little writing-room," reasoned Kennedy as we left the poor little hair-dresser quite exhausted by her narrative, "was next to the sanctum of Millefleur, where they found that bottle of ether phosphore and the oil of turpentine. Some one who knew of that note or perhaps wrote it must have reasoned that an answer would be written immediately. That person figured that the note would be the next thing written and that the top envelope of the pile would be used. That person knew of the deadly qualities of too much phosphorised ether, and painted the gummed flap of the envelope with several grains of it. The reasoning held good, for Agnes took the top envelope with its poisoned flap to Miss Blaisdell. No, there was no chance about that. It was all clever, quick reasoning."

"But," I objected, "how about the oil of turpentine?"

"Simply to remove the traces of the poison. I think you will see why that was attempted before we get through."

Kennedy would say no more, but I was content because I could see that he was now ready to put his theories, whatever they were, to the final test. He spent the rest of the day working at the hospital with Dr. Barron, adjusting a very delicate piece of apparatus down in a special room, in the basement. I saw it, but I had no idea what it was or what its use might be.

Close to the wall was a stereopticon which shot a beam of light through a tube to which I heard them refer as a galvanometer, about three feet distant. In front of this beam whirled a five-spindled wheel, governed by a chronometer which erred only a second a day. Between the poles of the galvanometer was stretched a slender thread of fused quartz plated with silver, only one one-thousandth of a millimetre in diameter, so tenuous that it could not be seen except in a bright light. It was a thread so slender that it might have been spun by a microscopic spider.

Three feet farther away was a camera with a moving film of sensitised material, the turning of which was regulated by a little flywheel. The beam of light focused on the thread in the galvanometer passed to the photographic film, intercepted only by the five spindles of the wheel, which turned once a second, thus marking the picture off into exact fifths of a second. The vibrations of the microscopic quartz thread were enormously magnified on the sensitive film by a lens and resulted in producing a long zig-zag, wavy line. The whole was shielded by a wooden hood which permitted no light, except the slender ray, to strike it. The film revolved slowly across the field, its speed regulated by the flywheel, and all moved by an electric motor.

I was quite surprised, then, when Kennedy told me that the final tests which he was arranging were not to be held at the hospital at all, but in his laboratory, the scene of so many of his scientific triumphs over the cleverest of criminals.

While he and Dr. Barren were still fussing with the machine he despatched me on the rather ticklish errand of gathering together all those who had been at the Novella at the time and might possibly prove important in the case.

My first visit was to Hugh Dayton, whom I found in his bachelor apartment on Madison Avenue, apparently waiting for me. One of O'Connor's men had already warned him that any attempt to evade putting in an appearance when he was wanted would be of no avail. He had been shadowed from the moment that it was learned that he was a patient of Millefleur's and had been at the Novella that fatal afternoon. He seemed to realise that escape was impossible. Dayton was one of those typical young fellows, tall, with sloping shoulders and a carefully acquired English manner, whom one sees in scores on Fifth Avenue late in the afternoon. His face, which on the stage was forceful and attractive, was not prepossessing at close range. Indeed it showed too evident marks of excesses, both physical and moral, and his hand was none too steady. Still, he was an interesting personality, if not engaging.

I was also charged with delivering a note to Burke Collins at his office. The purport of it was, I knew, a request couched in language that veiled a summons that Mrs. Collins was of great importance in getting at the truth, and that if he needed an excuse himself for being present it was suggested that he appear as protecting his wife's interests as a lawyer. Kennedy had added that I might tell him orally that he would pass over the scandal as lightly as possible and spare the feelings of both as much as he could. I was rather relieved when this mission was accomplished, for I had expected Collins to demur violently.

Those who gathered that night, sitting expectantly in the little armchairs which Kennedy's students used during his lectures, included nearly every one who could cast any light on what had happened at the Novella. Professor and Madame Millefleur were brought up from the house of detention, to which both O'Connor and Dr. Leslie had insisted that they be sent. Millefleur was still bewailing the fate of the Novella, and Madame had begun to show evidences of lack of the constant beautification which she was always preaching as of the utmost importance to her patrons. Agnes was so far recovered as to be able to be present, though I noticed that she avoided the Millefleurs and sat as far from them as possible.

Burke Collins and Mrs. Collins arrived together. I had expected that there would be an icy coolness if not positive enmity between them. They were not exactly cordial, though somehow I seemed to feel that now that the cause of estrangement was removed a tactful mutual friend might have brought about a reconciliation. Hugh Dayton swaggered in, his nervousness gone or at least controlled. I passed behind him once, and the odour that smote my olfactory sense told me too plainly that he had fortified himself with a stimulant on his way from the apartment to the laboratory. Of course O'Connor and Dr. Leslie were there, though in the background.

It was a silent gathering, and Kennedy did not attempt to relieve the tension even by small talk as he wrapped the forearms of each of us with cloths steeped in a solution of salt. Upon these cloths he placed little plates of German silver to which were attached wires which led back of a screen. At last he was ready to begin.

"The long history of science," he began as he emerged from behind the screen, "is filled with instances of phenomena, noted at first only for their beauty or mystery, which have been later proved to be of great practical value to mankind. A new example is the striking phenomenon of luminescence. Phosphorus, discovered centuries ago, was first merely a curiosity. Now it is used for many practical things, and one of the latest uses is as a medicine. It is a constituent of the body, and many doctors believe that the lack of it causes, and that its presence will cure, many ills. But it is a virulent and toxic drug, and no physician except one who knows his business thoroughly should presume to handle it. Whoever made a practice of using it at the Novella did not know his business, or he would have used it in pills instead of in the nauseous liquid. It is not with phosphorised ether as a medicine that we have to deal in this case. It is with the stuff as a poison, a poison administered by a demon."

Craig shot the word out so that it had its full effect on his little audience. Then he paused, lowered his voice, and resumed on a new subject.

"Up in the Washington Heights Hospital," he went on, "is an apparatus which records the secrets of the human heart. That is no figure of speech, but a cold scientific fact. This machine records every variation of the pulsations of the heart with such exquisite accuracy that it gives Dr. Barron, who is up there now, not merely a diagram of the throbbing organ of each of you seated here in my laboratory a mile away, but a sort of moving-picture of the emotions by which each heart here is swayed. Not only can Dr. Barron diagnose disease, but he can detect love, hate, fear, joy, anger, and remorse. This machine is known as the Einthoven 'string galvanometer,' invented by that famous Dutch physiologist of Leyden."

There was a perceptible movement in our little audience at the thought that the little wires that ran back of the screen from the arms of each were connected with this uncanny instrument so far away.

"It is all done by the electric current that the heart itself generates," pursued Kennedy, hammering home the new and startling idea. "That current is one of the feeblest known to science, for the dynamo that generates it is no ponderous thing of copper wire and steel castings. It is just the heart itself. The heart sends over the wire its own telltale record to the machine which registers it. The thing takes us all the way back to Galvani, who was the first to observe and study animal electricity. The heart makes only one three-thousandth of a volt of electricity at each beat. It would take over two hundred thousand men to light one of these incandescent lamps, two million or more to run a trolley-car. Yet just that slight little current is enough to sway the gossamer strand of quartz fibre up there at what we call the 'heart station.' So fine is this machine that the pulse-tracings produced by the sphygmograph, which I have used in other cases up to this time, are clumsy and inexact."

Again he paused as if to let the fear of discovery sink deep into the minds of all of us.

"This current, as I have said, passes from each one of you in turn over a wire and vibrates a fine quartz fibre up there in unison with each heart here. It is one of the most delicate bits of mechanism ever made, beside which the hairspring of a watch is coarse. Each of you in turn, is being subjected to this test. More than that, the record up there shows not only the beats of the heart but the successive waves of emotion that vary the form of those beats. Every normal individual gives what we call an 'electro-cardiogram,' which follows a certain type. The photographic film on which this is being recorded is ruled so that at the heart station Dr. Barron can read it. There are five waves to each heart-beat, which he letters P, Q, R, S, and T, two below and three above a base line on the film. They have all been found to represent a contraction of a certain portion of the heart. Any change of the height, width, or time of any one of those lines shows that there is some defect or change in the contraction of that part of the heart. Thus Dr. Barron, who has studied this thing carefully, can tell infallibly not only disease but emotion."

It seemed as if no one dared look at his neighbour, as if all were trying vainly to control the beating of their own hearts.

"Now," concluded Kennedy solemnly as if to force the last secret from the wildly beating heart of some one in the room, "it is my belief that the person who had access to the operating-room of the Novella was a person whose nerves were run down, and in addition to any other treatment that person was familiar with the ether phosphore. This person knew Miss Blaisdell well, saw her there, knew she was there for the purpose of frustrating that person's own dearest hopes. That person wrote her the note, and knowing that she would ask for paper and an envelope in order to answer it, poisoned the flap of the envelope. Phosphorus is a remedy for hysteria, vexatious emotions, want of sympathy, disappointed and concealed affections—but not in the quantities that this person lavished on that flap. Whoever it was, not life, but death, and a ghastly death, was uppermost in that person's thoughts."

Agnes screamed. "I saw him take something and rub it on her lips, and the brightness went away. I—I didn't mean to tell, but, God help me, I must."

"Saw whom?" demanded Kennedy, fixing her eye as he had when he had called her back from aphasia.

"Him—Millefleur—Miller," she sobbed, shrinking back as if the very confession appalled her.

"Yes," added Kennedy coolly, "Miller did try to remove the traces of the poison after he discovered it, in order to protect himself and the reputation of the Novella."

The telephone bell tinkled. Craig seized the receiver.

"Yes, Barron, this is Kennedy. You received the impulses all right?
Good. And have you had time to study the records? Yes? What's that?
Number seven? All right. I'll see you very soon and go over the records
again with you. Good-bye."

"One word more," he continued, now facing us. "The normal heart traces its throbs in regular rhythm. The diseased or overwrought heart throbs in degrees of irregularity that vary according to the trouble that affects it, both organic and emotional. The expert like Barron can tell what each wave means, just as he can tell what the lines in a spectrum mean. He can see the invisible, hear the inaudible, feel the intangible, with mathematical precision. Barron has now read the electro-cardiograms. Each is a picture of the beating of the heart that made it, and each smallest variation has a meaning to him. Every passion, every emotion, every disease, is recorded with inexorable truth. The person with murder in his heart cannot hide it from the string galvanometer, nor can that person who wrote the false note in which the very lines of the letters betray a diseased heart hide that disease. The doctor tells me that that person was number—"

Mrs. Collins had risen wildly and was standing before us with blazing eyes. "Yes," she cried, pressing her hands on her breast as if it were about to burst and tell the secret before her lips could frame the words, "yes, I killed her, and I would follow her to the end of the earth if I had not succeeded. She was there, the woman who had stolen from me what was more than life itself. Yes, I wrote the note, I poisoned the envelope. I killed her."

All the intense hatred that she had felt for that other woman in the days that she had vainly striven to equal her in beauty and win back her husband's love broke forth. She was wonderful, magnificent, in her fury. She was passion personified; she was fate, retribution.

Collins looked at his wife, and even he felt the spell. It was not crime that she had done; it was elemental justice.

For a moment she stood, silent, facing Kennedy. Then the colour slowly faded from her cheeks. She reeled.

Collins caught her and imprinted a kiss, the kiss that for years she had longed and striven for again. She looked rather than spoke forgiveness as he held her and showered them on her.

"Before Heaven," I heard him whisper into her ear, "with all my power as a lawyer I will free you from this."

Gently Dr. Leslie pushed him aside and felt her pulse as she dropped limply into the only easy chair in the laboratory.

"O'Connor," he said at length, "all the evidence that we really have hangs on an invisible thread of quartz a mile away. If Professor Kennedy agrees, let us forget what has happened here to-night. I will direct my jury to bring in a verdict of suicide. Collins, take good care of her." He leaned over and whispered so she could not hear. "I wouldn't promise her six weeks otherwise."

I could not help feeling deeply moved as the newly reunited Collinses left the laboratory together. Even the bluff deputy, O'Connor, was touched by it and under the circumstances did what seemed to him his higher duty with a tact of which I had believed him scarcely capable. Whatever the ethics of the case, he left it entirely to Dr. Leslie's coroner's jury to determine.

Burke Collins was already making hasty preparations for the care of his wife so that she might have the best medical attention to prolong her life for the few weeks or months before nature exacted the penalty which was denied the law.

"That's a marvellous piece of apparatus," I remarked, standing over the connections with the string galvanometer, after all had gone. "Just suppose the case had fallen into the hands of some of these old-fashioned detectives—"

"I hate post-mortems—on my own cases," interrupted Kennedy brusquely. "To-morrow will be time enough to clear up this mess. Meanwhile, let us get this thing out of our minds."

He clapped his hat on his head decisively and deliberately walked out of the laboratory, starting off at a brisk pace in the moonlight across the campus to the avenue where now the only sound was the noisy rattle of an occasional trolley car.

How long we walked I do not know. But I do know that for genuine relaxation after a long period of keen mental stress, there is nothing like physical exercise. We turned into our apartment, roused the sleepy hall-boy, and rode up.

"I suppose people think I never rest," remarked Kennedy, carefully avoiding any reference to the exciting events of the past two days. "But I do. Like every one else, I have to. When I am working hard on a case—well, I have my own violent reaction against it—more work of a different kind. Others choose white lights, red wines and blue feelings afterwards. But I find, when I reach that state, that the best anti-toxin is something that will chase the last case from your brain by getting you in trim for the next unexpected event."

He had sunk into an easy chair where he was running over in his mind his own plans for the morrow.

"Just now I must recuperate by doing no work at all," he went on slowly undressing. "That walk was just what I needed. When the fever of dissipation comes on again, I'll call on you. You won't miss anything, Walter."

Like the famous Finnegan, however, he was on again and gone again in the morning. This time I had no misgivings, although I should have liked to accompany him, for on the library table he had scrawled a little note, "Studying East Side to-day. Will keep in touch with you. Craig." My daily task of transcribing my notes was completed and I thought I would run down to the Star to let the editor know how I was getting along on my assignment.

I had scarcely entered the door when the office boy thrust a message into my hand. It stopped me even before I had a chance to get as far as my own desk. It was from Kennedy at the laboratory and bore a time stamp that showed that it must have been received only a few minutes before I came in.

"Meet me at the Grand Central," it read, "immediately."

Without going further into the office, I turned and dropped down in the elevator to the subway. As quickly as an express could take me, I hurried up to the new station.

"Where away?" I asked breathlessly, as Craig met me at the entrance through which he had reasoned I would come. "The coast or Down East?"

"Woodrock," he replied quickly, taking my arm and dragging me down a ramp to the train that was just leaving for that fashionable suburb.

"Well," I queried eagerly, as the train started. "Why all this secrecy?"

"I had a caller this afternoon," he began, running his eye over the other passengers to see if we were observed. "She is going back on this train. I am not to recognise her at the station, but you and I are to walk to the end of the platform and enter a limousine bearing that number."

He produced a card on the back of which was written a number in six figures. Mechanically I glanced at the name as he handed the card to me. Craig was watching intently the expression on my face as I read, "Miss Yvonne Brixton."

"Since when were you admitted into society?" I gasped, still staring at the name of the daughter of the millionaire banker, John Brixton.

"She came to tell me that her father is in a virtual state of siege, as it were, up there in his own house," explained Kennedy in an undertone, "so much so that, apparently, she is the only person he felt he dared trust with a message to summon me. Practically everything he says or does is spied on; he can't even telephone without what he says being known."

"Siege?" I repeated incredulously. "Impossible. Why, only this morning I was reading about his negotiations with a foreign syndicate of bankers from southeastern Europe for a ten-million-dollar loan to relieve the money stringency there. Surely there must be some mistake in all this. In fact, as I recall it, one of the foreign bankers who is trying to interest him is that Count Wachtmann who, everybody says, is engaged to Miss Brixton, and is staying at the house at Woodrock. Craig, are you sure nobody is hoaxing you?"

"Read that," he replied laconically, handing me a piece of thin letter-paper such as is often used for foreign correspondence. "Such letters have been coming to Mr. Brixton, I understand, every day."

The letter was in a cramped foreign scrawl:

JOHN BRIXTON, Woodrock, New York.

American dollars must not endanger the peace of Europe. Be warned in time. In the name of liberty and progress we have raised the standard of conflict without truce or quarter against reaction. If you and the American bankers associated with you take up these bonds you will never live to receive the first payment of interest.

THE RED BROTHERHOOD OF THE BALKANS.

I looked up inquiringly. "What is the Red Brotherhood?" I asked.

"As nearly as I can make out," replied Kennedy, "it seems to be a sort of international secret society. I believe it preaches the gospel of terror and violence in the cause of liberty and union of some of the peoples of southeastern Europe. Anyhow, it keeps its secrets well. The identity of the members is a mystery, as well as the source of its funds, which, it is said, are immense."

"And they operate so secretly that Brixton can trust no one about him?"
I asked.

"I believe he is ill," explained Craig. "At any rate, he evidently suspects almost every one about him except his daughter. As nearly as I could gather, however, he does not suspect Wachtmann himself. Miss Brixton seemed to think that there were some enemies of the Count at work. Her father is a secretive man. Even to her, the only message he would entrust was that he wanted to see me immediately."

At Woodrock we took our time in getting off the train. Miss Brixton, a tall, dark-haired, athletic girl just out of college, had preceded us, and as her own car shot out from the station platform we leisurely walked down and entered another bearing the number she had given Kennedy.

We seemed to be expected at the house. Hardly had we been admitted through the door from the porte-cochere, than we were led through a hall to a library at the side of the house. From the library we entered another door, then down a flight of steps which must have brought us below an open courtyard on the outside, under a rim of the terrace in front of the house for a short distance to a point where we descended three more steps.

At the head of these three steps was a great steel and iron door with heavy bolts and a combination lock of a character ordinarily found only on a safe in a banking institution.

The door was opened, and we descended the steps, going a little farther in the same direction away from the side of the house. Then we turned at a right angle facing toward the back of the house but well to one side of it. It must have been, I figured out later, underneath the open courtyard. A few steps farther brought us to a fair-sized, vaulted room.