It was apparent that quick action was necessary if the mystery was ever to be solved. Kennedy evidently thought so, too, for he did not wait even until he returned to his laboratory to set in motion, through our old friend, Commissioner O'Connor, the machinery that would result in warrants to compel the attendance at the laboratory of all those interested in the case. Then he called up Dr. Leslie and finally Dr. Blythe himself.

Back again in the laboratory, Kennedy employed the time in developing some plates of the pictures he had taken, and by early evening, after a brief study of them, his manner indicated that he was ready.

Dr. Leslie, whom he had asked to come a little before the rest, arrived early, and a few moments later Dr. Blythe, very much excited by the message he had received.

"Have you found anything?" he asked eagerly. "I've been trying all sorts of tests myself, and I can't prove the presence of a thing—not a thing."

"Not ergot?" asked Kennedy quietly.

"No," he cried, "you can't prove anything—you can't prove that she was poisoned by ergot."

Dr. Leslie looked helplessly at Kennedy, but said nothing.

"Not until recently, perhaps, could I have proved anything," returned Kennedy calmly. "Evidently you didn't know, Dr. Blythe, that the first successful isolation of an alkaloid of ergot from the organs in a case of acute ergotism had been made by two Pittsburgh scientists. True, up to the present toxicologists had to rely on the physical properties of this fungus of rye for its identification. That may have made it seem like a safe poison to someone. But I have succeeded in isolating ergotinin from the sample of the contents of the organs of the poor girl."

Without pausing, he picked up a beaker. "Here I have the residue left from an acid solution of an extract of the organs, treated with chloroform. It is, as you see, crystalline."

In his other hand he held up another beaker. "Next I got the residue obtained by extraction of the acid aqueous liquid with ether. That, too, is crystalline."

Kennedy displayed something in the shape of long needles, the sides of which were not quite parallel and the ends replaced by a pair of faces.

Quickly he dissolved some of the crystals in sulphuric acid. Then he added another chemical from a bottle labeled ferro chlorid. The liquid, as we bent over it, changed quickly to a brilliant orange, then a crimson, next a green, and finally became a deep blue.

"What he has derived from the body responds to all the chemical tests for ergotinin itself," remarked Dr. Leslie, looking quickly across at Dr. Blythe.

Dr. Blythe said nothing.

I smelt of the stuff. Odors with me, as, I suppose, with other people, have a psychological effect, calling up scenes associated with them. This odor recalled something. I strove to recollect what it was. At last it came with a rush.

"The meat sauce!" I exclaimed involuntarily.

"Exactly," replied Kennedy. "I have obtained that bottle. There was ergot in it, cleverly concealed by the natural smell and taste of the sauce. But who put it there? Who had the knowledge that would suggest using such a poison? Who had the motive? Who had been dining with her that fatal evening?"

Kennedy had no chance to answer his questions, even if he had intended to do so.

The door of the laboratory opened and Rita Tourville, in charge of one of O'Connor's men, who looked as if he might have enjoyed it better if the lady had not been so angry, entered. Evidently O'Connor had timed the arrival closely to what Craig had asked, for scarcely a moment later Faber came whirling up in one of his own cars. Not a word passed between him and Rita, yet I felt sure that they had some understanding of each other. Leila arrived shortly, and it was noticeable that Rita avoided her, though for what reason I could not guess. Finally came Jacot, blustering, but, having made the officer the safety-valve of his mercurial feelings, quickly subsiding before us. Dr. Blythe appeared amazed at the quickness with which Kennedy moved now.

"In ordinary times," began Kennedy, noting as he spoke the outward attitude of our guests toward each other, "the world would have stood aghast at the disappearance of such a masterpiece as the FÊte by Watteau. It would have ranked with the theft of Gainesborough's Duchess of Devonshire, Da Vinci's Mona Lisa, the brown-skinned Madonna of the Mexican convent, Millet's Goose-girl, and the Shepherd and Flock, the portrait of Saskia by Rembrandt, and other stolen masterpieces.

"But today the vicissitudes of works of art in war time pass almost unnoticed. Still there is a fascination exercised over the human mind by works of art and other objects of historic interest, the more so because the taking of art treasures seems to have become epidemic in northern Europe."

He laid down what looked more like two rough sketches than photographs, yet they were photographs, though the relative brightness of color in photographs was quite different. Outlines were displaced, also. Ugly spots and bands marred the general effect. They were peculiar.

"They are X-ray images or radiographs of two oil paintings, both claimed to be copies of Watteau's famous FÊte," explained Kennedy, picking up one of them.

"In a radiograph of the body," he continued, "the difference of brightness that distinguishes the heart from the lungs, bones from flesh, is due to the different densities of tissues. In these pictures the same effect is produced by the different densities of the pigments, especially of their principal and heaviest elements."

He paused and laid down a chart. "For anyone who doubts what I am about to prove, I have made a scale of oil colors arranged in accordance to their transparency to Roentgen rays by applying standard pigments to canvas in patches of equal thickness.

"I think you can see what I am driving at. For instance, a design drawn in a heavy pigment will show through a layer of a less dense pigment, under the influence of the X-ray—just as bones show through flesh. In other words, an ordinary photograph reproduces only the surface of a painting. A radiograph represents all the pigments underneath, also producing effects in proportion to their densities.

"Let me show you the practical result of all this in studying such radiographs, as worked out by a German student. I have made several very interesting and conclusive discoveries which these radiographs I have taken illustrate."

He paused a moment, for the sake of emphasis. "You will notice," he resumed carefully, "the lace frill above the bodice on the figure of Madame de Montespan, in this radiograph. In the painting the frill is sharply defined and can be clearly distinguished from the bodice. But look at this radiograph. It appears tattered. It overflows the bodice.

"That led me to suspect that the bodice was widened as an afterthought—perhaps to diminish the area of white. That is the reason why the white shows through the bodice in the radiograph. But in this other one the bodice and the frill are substantially as they must be in the original."

Again he paused, as if taking up a new point. "This radiograph,—number one, I may call it—shows a broad light band on the right hand of the figure, of which not a trace is to be found either in the other radiograph or the painting itself. It represents the first rough sketch of an arm and hand.

"Again, in this first radiograph the ring and little fingers are close together and a sixth finger appears between the index and middle fingers. From that I infer that the hand hung limp with the fingers nearly in contact in the first sketch and that the fingers were afterward separated. But in this second radiograph the arm, hand and fingers are perfect."

It was fascinating to listen to Kennedy as he delved down into the invisible beneath the very oils and dug out their hidden mystery.

"Take the head and shoulder," he continued. "Radiograph number one clearly shows flaking of the painting which has been painted over to conceal it. Ordinary light reveals no trace, either, of a long crack on the shoulder which evidently was filled with a thick mass of pigment containing too little white lead to obliterate the crack in the radiograph. White spots above the ear, in the radiograph, probably indicate an excess of white lead used in retouching. At any rate, radiograph number two contains no such defects."

Kennedy paused before drawing the conclusion. "The radiograph of an original picture reveals changes made by the artist in the course of his work. The counterfeiter, like other copyists, reproduces as accurately as possible the final result. That is all he can see. He makes errors and corrections, but of a different kind. There are no serious changes.

"So, a radiograph of even a part of a picture shows the layers of pigment that are hidden from the eye and the changes made during the composition of the work. One can easily distinguish the genuine from the spurious copies, for it is absolutely impossible for an imitator to make a copy that will stand the X-ray test.

"You see," he went on enthusiastically, "the most striking feature of these radiographs is their revelation of details of the first sketch, which have been altered in the finished picture. We actually obtain an insight into the methods of an artist—" he paused, adding—"who has been dead for centuries."

It was wonderful what Kennedy was getting out of those, to us, blurred and indistinct skiagraphs. I studied the faces before me. None seemed to indicate any disposition to break down. Kennedy saw it, too, and evidently determined to go to the bitter end in hammering out the truth of the mystery.

"One moment more, please," he resumed. "The radiograph shows even more than that. It shows the possibility of detecting a signature that has been painted over, in order to disarm suspicion. The detection is easier in proportion to the density of the pigment used for the signature and the lack of density of the superposed coat."

He had laid the radiographs on the table before him, with a finger on the corner of each, as he faced us.

"At the bottom of each of the paintings in question," he shot out, leaning forward, "you will find nothing in the way of a signature. But here, in radiograph number two, for instance, barely discernible, are the words, "R. Fleming," quite invisible to the eye, but visible to the X-ray. These words have been painted over. Why? Was it to prevent anyone from thinking that the owner had ever had any connection with Rhoda Fleming?"

I was following Kennedy, but not so closely that I missed a fearful glance of Rita from Faber to Jacot. What it meant, I did not know. The others were too intent on Kennedy's exposure to notice. I wondered whether someone had sought to conceal the fact that he had a copy of the famous Watteau, made by Miss Fleming?

"Look at the bottom of the other radiograph, number one, further toward the left," pursued Kennedy resistlessly. "There you will discover traces of an 'A' and a 'W,' which do not appear on the painting. Between these two are marks which can also be deciphered by the X-ray—'Antoine Watteau.' Perhaps it was painted over lightly so that an original could be smuggled in as a copy. More likely it was done so that a thief and murderer could not be traced."

As Kennedy's voice rang out, more and more accusatory, Rita Tourville became more and more uncontrollably nervous.

"It was suggested," modulated Kennedy, playing with his little audience as a cat might with a mouse, "that someone murdered Rhoda Fleming with the little-understood poison, ergot, because of an infatuation for the picture itself. But the modern crook has an eye for pictures, just as for other valuables. The spread of the taste for art has taught these fellows that such things as old masters are worth money, and they will even murder now to get them. No, that radiograph which I have labeled number one is not a copy. It is of the genuine old master—the real Watteau.

"Someone, closely associated with Miss Fleming, had found out that she had the original. That person, in order to get it, went even so far as to—"

Rita Tourville jumped up, wildly, facing Craig and crying out, "No, no—his is the copy—the copy by Miss Fleming. It was I who told him to paint over the signature. It was I who called him away—both nights—on a pretext—when he was dining with her—alone—called him because—I—I loved him and I knew—"

Faber was on his feet beside her in a moment, his face plainly showing his feelings toward her. As he laid his hand on her arm to restrain her, she turned and caught a penetrating glance from Jacot's hypnotic eye.

Slowly she collapsed into her chair, covering her face with her hands, sobbing. For a moment a look of intense scorn and hatred blazed in Leila's face, then was checked.

Craig waved the radiograph of the real Watteau as he emphasized his last words.

"In spite of Rita Tourville's unexpected love for Faber, winning him from your victim, and with the aid of your wife, Leila, in the rÔle of maid, the third member of your unique gang of art thieves, you are convicted infallibly by my X-ray detective," thundered Craig as he pointed his finger at the now cowering Jacot.