Mackay and I exchanged glances. Kennedy busied himself putting away some of the more important bits of evidence in the case, placing the tiny tubes of solution, the blood smears, and other items together in a cabinet at the farther corner of the laboratory. The vast bulk of his paraphernalia, the array of glass and chemicals and instruments, he left on the table for the morning. Then he faced us again, with a smile.

"Suppose you start up the percolator once more, Walter!" He took a cigar and lighted it from the match I struck. "I believe I've earned another cup of coffee," he added.

Mackay had been fidgeting considerably since Kennedy's explanation of the possible danger to Shirley, as well as to ourselves or even to others.

"Isn't there something we can do, Kennedy?" he exclaimed, suddenly. "Is it necessary to sit back and wait for this unknown to strike again?"

"Ordinarily," Kennedy replied, "on a case like this it has been my custom to permit the guilty parties to betray themselves, as they will do inevitably—especially when I call to my aid the recent discoveries of science for the detection and measurement of fine and almost imperceptible shades of emotion. But now that I realize the presence of this menace I shall become a detective of action; in fact, I shall not stop at any course to hurry matters. The very first thing in the morning I shall go to the studio and I want you and Jameson along. I"—his eyes twinkled; it was the excitement at the prospect—"I may need considerable help in getting the evidence I wish."

"Which is—?" It was I who interposed the question.

Kennedy blew a cloud of smoke. "There are three ways of tracing down a crime, aside from the police method of stool pigeons to betray the criminals and the detective bureau method of cross-examination under pressure, popularly known as the third degree."

"What are they?" Mackay asked, unaware that Kennedy needed little prompting once he felt inclined to talk out some matter puzzling him.

"One is the process of reasoning from the possible suspects to the act itself—in other words, putting the emphasis on the motive. A second is the reverse of the first, involving a study of the crime for clues and making deductions from the inevitable earmarks of the person for the purpose of discovering his identity. The third method, except for some investigations across the water, is distinctly my own, the scientific.

"In all sciences," Kennedy went on, warming to his subject, "progress is made by a careful tabulation of proved facts. The scientific method is the method of exact knowledge. Thus, in crime, those things are of value to us which by an infinite series of empiric observations have been established and have become incontrovertible. The familiar example, of course, is fingerprints. Nearly everyone knows that no two men have the same markings; that the same man displays a pattern which is unchanging from birth to the grave.

"No less certain is the fact that human blood differs from the blood of animals, that in faint variations the blood of no two people is alike, that the blood of any living thing, man or beast, is affected by various things—an infinite number almost—most of which are positively known to modern medical investigators.

"In this case my principal scientific clue is the blood left upon the portiere by the man who took the needle the night following the murder. Next in importance is the fact, demonstrated by me, that some one at the studio wiped a hypodermic on a towel after inoculating himself with antivenin. Of course I am presuming that this latter man inoculated himself and not some one else, because it is obvious. If necessary I can prove it later, however, by analyzing the trace of blood. That is not the point. The point is that whoever removed the needle pricked himself and yet did not die of the venom—unless it was a person not under our observation, an unlikely premise. Therefore, because of this last fact, and because again it is obvious, I expect to find that the same individual inoculated himself with antivenin and removed the needle from the portiere; and I expect to prove it beyond possibility of doubt by an analysis of his blood. A sample of the blood from this person will be identical with the spot on the portiere, and—much the easier test—will contain traces of the antitoxin.

"With that much accomplished, a little of the, well—third degree, will bring about a confession. It is circumstantial evidence of the strongest sort. Not only does a man take precautions against a given poison, but he is proved to be the one who removed the needle actually responsible for Miss Lamar's death.

"My handicap, however, is that I have no justifiable excuse for taking a sample of blood from each of the people we suspect, or feel we might suspect. For that reason I was waiting until one of the other detective methods should narrow the field of suspicion. Now that there is the menace of another attempt to take a life I am forced to act. To-morrow we will get samples of blood from everyone by artifice—or force!

"Meanwhile—" He hastened to continue, as though afraid we might interrupt to break his train of thought. "Meanwhile, to-night, let us see if it is possible to accomplish something by the deductive method.

"Already I have gone into an analysis starting from the nature of the crime and reasoning to the type of criminal responsible. The guilty man—or woman—is a person of high intelligence, added to genuine cleverness. But for the results accomplished in this laboratory we would be without a clue; our hands would be tied completely. Both Miss Lamar and Werner were killed by unusual poisons; deadly, and almost impossible to trace. There was a crowd of people about in each case; yet we have no witnesses. Now who, out of all our people with possible motives, are intelligent enough and clever enough to be guilty?"

Kennedy glanced first at me, then at Mackay.

"Manton? Phelps?" suggested the district attorney.

"The promoter," Kennedy rejoined, "is the typical man of the business world beneath the eccentricity of manner which seems to cling to everyone in the picture field. Ordinarily his type, thinking in millions of dollars and juggling nickel and dime admissions or other routine of commercial detail is apart from the finer subtle passions of life. When a business man commits murder he generally uses a pistol because he is sure it is efficient—he can see it work. The same applies to Phelps."

"Millard?" Mackay hesitated now to face the logic of Kennedy's keen mind. "He was Stella Lamar's husband!"

"Millard is a scenario writer and so apt to have a brain cluttered with all sorts of detail of crime and murder. At the same time an author is so used to counterfeiting emotion in his writings that he seldom takes things seriously. Life becomes a joke and Millard in particular is a butterfly, concerned more with the smiles of extra girls and the favor of Miss Faye than the fate of the woman whose divorce from him was not yet complete. A writer is the other extreme from the business man. The creator of stories is essentially inefficient because he tries to feel rather than reason. When an author commits murder he sets a stage for his own benefit. He is careful to avoid witnesses because they are inconvenient to dispose of. At the same time he wants the victim to understand thoroughly what is going to happen and so he is apt to accompany his crime with a speech worded very carefully indeed. Then he may start with an attempt to throttle a person and end up with a hatchet, or he may plan to use a razor and at the end brain his quarry with a chair. He lives too many lives to follow one through clearly—his own."

"How about Shirley?" I put in.

"At first glance Shirley and Gordon suggest themselves because both murders were highly spectacular, and the actor, above everything else, enjoys a big scene. After Werner's death, for instance, Shirley literally strutted up and down in that set. He was so full of the situation, so carried away by the drama of the occasion, that he failed utterly to realize how suspicious his conduct would seem to an observer. Unfortunately for our hypotheses, the use of venom and toxin is too cold-bloodedly efficient. The theatrical temperament must have emotion. An actor cruel and vicious enough to strike down two people as Miss Lamar and Werner were stricken, of sufficient dramatic make-up to conceive of the manner of their deaths, would want to see them writhe and suffer. He would select poisons equally rare and effective, but those more slow and painful in their operation. No, Walter, Shirley is not indicated by this method of reasoning. The arrangement of the scenes for the murders was simply another detail of efficiency, not due to a wish to be spectacular. The crowd about in each case has added greatly to the difficulty of investigation."

"Do you include Gordon in that?" Mackay asked.

"Yes, and in addition"—Kennedy smiled slightly—"I believe that Gordon is rather stupid. For one thing, he has had several fights in public, at the Goats Club and at the Midnight Fads and I suppose elsewhere. That is not the clever rogue. Furthermore, he had been speculating, not just now and then, but desperately, doggedly. Clever men speculate, but scientific men never. Our unknown criminal is both clever and intelligent."

"That brings you to the girls, then," Mackay remarked.

Kennedy's face clouded and I could see that he was troubled. "To be honest in this one particular method of deduction," he stated, "I must admit that both Miss Faye and Miss Loring are worthy of suspicion. The fact of their rise in the film world, the evidences of their popularity, is proof that they are clever. Miss Loring, in my few brief moments of contact with her on two occasions, showed a grasp of things and a quickness which indicate to me that she possesses a rare order of intelligence for a woman. As for Miss Faye"—again he hesitated—"one little act of hers demonstrated intelligence. When Shirley was standing guard in the set after Werner's death, and making a fool of himself, Millard evidently wanted to get over and speak to him, perhaps to tell him not to let me find him searching the scene as though his life depended upon it, perhaps something else. But Miss Faye stopped him. Unquestionably she saw that anyone taking an interest in the remains of the banquet just then would become an object of suspicion."

"Do you really suspect Marilyn or Enid?" I inquired.

"If this were half a generation ago I would say without hesitation that the crime was the handiwork of a man. But now the women are in everything. Young girls particularly—" He shrugged his shoulders.

Mackay had one more suggestion. "The camera men, the extras, the technical and studio staffs—they are not worthy of consideration, are they?"

Kennedy shook his head.

The odor of coffee struck my nostrils and I turned to find the percolator steaming. Kennedy leaned over, to take a whiff. Mackay rose. At that moment there was a sudden crash and the window-pane was shattered. Simultaneously a flash of light and a deafening explosion took place in the room, scattering broadcast tiny bits of glass from the laboratory table, splashing chemicals, many of them dangerous, over everything.

Kennedy hurried to the wreck of his paraphernalia. In an instant he held up a tiny bit of jagged metal.

"An explosive bullet!" he exclaimed. "An attempt to destroy my evidence!"