They drove in silence to headquarters, each man busy with his thoughts. It was not until they were alone in Leverage's sanctum that the subject of the recent interview was again broached. It was Leverage who brought it up, in his characteristically gruff way.

"I reckon you're wonderin', Carroll, about what I said back yonder in the car?"

"About arresting Barker?"

"Yes. I guess you're figuring what I'd arrest him for, eh?"

"I'm interested—yes."

"I'd arrest him for this." Leverage leaned forward earnestly, his attitude that of a man eager to convince. "Let's admit right off the reel that the skirt in the taxicab croaked Warren. Looks like she did, anyway; but whether she did or not, it's an even bet that there was a man mixed up in it somewhere. And if that man isn't Mr. William Barker, then I'll eat a month's pay."

"You're sure there was a man mixed up somewhere?"

"Certainly. This murder deal was planned in advance. It must have been. Things couldn't just work out that way. And no woman, no matter how much she wanted to bump Warren off, could think of a thing that complicated. Even if she did think of it, she wouldn't have the nerve to carry it out that way. Ain't I right?"

"You may not be right, Leverage; but you're certainly logical."

"Good! Now, so far, we ain't got any man in this case except Barker."

Carroll shook his head.

"You're wrong there."

"How?"

"Somewhere in this town is some man who is interested in the woman with whom Warren was planning to elope. Don't forget this, Leverage—I let Barker ramble on. I like to hear 'em talk. The minute he jumped at the idea that the woman in the taxi was Miss Gresham, I knew perfectly well that he knew she was not. I also believe that he knows who the woman was. Further, I believe that she is socially prominent. That being the case, it is a safe guess that there is some man who might commit a murder, provided he knew in advance of the elopement. Our task now is to discover that woman and, through her, the man interested."

Leverage frowned thoughtfully.

"Listens good," he volunteered at length. "Another thing—Barker admits he was shooting pool in Kelly's place last night around midnight; and Kelly's place is only half a block from the Union Station. That sounds significant!"

"It does; and then again it may mean nothing. What I am striving for is to make William Barker feel that he is safe. The safer he feels, the more readily he will talk. No matter how many lies he tells, everything that he says is of value. He didn't know, of course, that we already had a perfect alibi for Miss Gresham; but even if we hadn't, his assumed belief that she committed the crime would have assured me that she did not. No-o, I think we'd better not arrest the man unless he forces our hand—tries to jump town, or something like that. Better let him remain at large and talk frequently. If he has anything to betray, there's more chance that he'll do it that way. Don't you think I'm right?"

"I wouldn't admit it if I didn't, Carroll. I've seen you in action too often to believe you're ever wrong."

Carroll flushed boyishly.

"Don't be absurd, Leverage! I'm often wrong—very wrong. And don't think that I'm a transcendent detective; they don't really exist, you know. I'm merely trying to be human, to learn the nature of the people with whom I'm dealing. I try to learn 'em as well as they know themselves—maybe a little better; and then I try to separate the wheat of vital facts from the chaff of the inconsequential."

"Just the same," insisted Leverage loyally, "you always get 'em!"

"And when I do, it is because I have used nothing more than plain common sense. Don't think that I attach no importance to physical clues. They're immensely valuable; but the one weakness in a criminal is his lack of common sense. His perspective is awry, his sense of values distorted. Usually he bothers his head about a myriad minor details, and pays but scant attention to the genuinely important things. It is upon that weakness that I am banking—particularly so in the case of Barker."

"I insist that you're a wonder, Carroll!"

"And I insist that you're foolishly complimentary. Did you ever stop to realize, Eric, that when a crime is committed the advantage lies entirely with the detective? The detective can make a thousand mistakes during the course of his investigations and still trap his man; but the criminal cannot make one single error—not one!"

"Maybe so, David; but it takes a good man to recognize that one, and to know what to do with it."

Carroll grinned and left, and then for two days devoted himself to a study of the conditions surrounding the murder—that and routine matters. The trunk, for instance, was duly returned by the railroad from New York, and Carroll and his friend made a minute investigation of every article contained therein. Their search was well-nigh fruitless. The trunk contained little save the wardrobe of a well-dressed man—suits, shirts, underwear, shoes, caps. There were also golf and tennis togs; a few books; a handsome leather secretary, containing a good many personal letters and one or two business missives which were of little interest. Altogether the examination of the trunk—a process which occupied three hours—established nothing definite, save that there was nothing to be discovered. Its results were hopelessly negative.

Meanwhile the city sizzled with gossip of the Warren murder. The seemingly impenetrable mystery surrounding the case, its many sensational features, the admission of the police department that the woman in the case was not Hazel Gresham, fiancÉe of the dead man, yet the certainty that there was a woman, and that she was of the better class—all this served to keep the tongues of men and women alike wagging at both ends.

Carroll was besieged with anonymous letters. Dozens of prominent married women were mentioned as having been, at one time or another, the object of Warren's amorous attentions. Carroll read each one carefully and filed it away. He had hoped for this, but the results had far exceeded his expectations, and he found himself bewildered rather than assisted by the response from nameless individuals who were morbidly eager to be of help.

The detective knew that the running down of each individual trail—the investigation of each of Warren's supposed affairs of the heart—would be an interminable procedure. And so far not a single one of the letters had varied from another. They connected Warren's name with that of some married woman, and let it go at that. It was quite evident that the dead man had been very much of a Lothario; too much so for the mental ease of the investigator who was struggling to link the cause of his death with one particular affair.

The reporters allowed their imaginations to run wild. The story was what is known, in the parlance of the newspaper world, as a "space-eater." City editors turned their best men loose on it and devoted columns to conjecture. There was little definite information upon which to base the daily stories that were luridly hurled into type. Thus far Spike Walters, driver of taxicab No. 92,381, was the only person under arrest, and only those persons too lazy to exercise their minds were willing to believe that Spike was guilty or that he knew more of the crime than he had told.

Carroll read each news story attentively. No wild theory of a pop-eyed reporter, hungry for fact, was too absurd to receive his careful attention. But they proved of little assistance. With the spot-light of publicity blazing on the crime, the investigation seemed to have become static. There was no forward movement; nothing save that in the brain of David Carroll salient facts were being seized upon and meticulously catalogued for future reference.

Cartwright and Reed, the plain-clothes men detailed to shadow William Barker, reported nothing suspicious in that gentleman's movements. He seemed to be making no effort to secure employment, but, on the other hand, there was little of interest in what he did do. Again the stone wall of negative action.

Barker spent his mornings in his boarding-house, apparently luxuriating in long slumbers; he ate always at the same cheap restaurant; and his afternoons and evenings were devoted largely to the science of eight-ball pool at Kelly's place. There may have been significance in his loyalty to Kelly's place; but if there was, it was too vague for Carroll to consider. He merely remembered the fact that Barker was a steady patron of the pool-room near the Union Station, and filed it away with his other threads of information concerning the murder.

Carroll was frankly puzzled. The case differed widely from any other with which he had ever come in contact. Usually there was an array of persons upon whom suspicion could be justly thrown; a collection of suspects from whom the investigator could take his choice, or from whom he could extract facts which eventually might be used to corner the guilty person. In the present case there was no one to whom he could turn an accusing finger.

Of course, he was convinced that William Barker knew a great deal about the crime and the events which preceded it; but Barker wouldn't talk—and he, Carroll, had no evidence that enabled him to bluff, to draw Barker out against his will.

The crime seemed to have lost itself in the sleety cold of the December midnight upon which it was committed. The trails were not blind—there were simply no trails. The circumstances baffled explanation—a lone woman entering an empty taxicab; a run to a distant point in the city; the discovery of the woman's disappearance, and in her stead the sight of the dead body of a prominent society man—that, and the further blind information that the suit-case which the woman had carried was the property of the man whose body was huddled horribly in the taxicab.

The woman, whoever she was, had either been unusually clever or unusually lucky. Minute examination of the interior of the cab had revealed nothing—not a fingerprint, nor a scrap of handkerchief. There was absolutely nothing which could serve as a clue in establishing her identity.

And yet, somewhere in the city—a city of two hundred thousand souls—was the woman who could clear up the mystery.

Convinced that she was prominent socially, Carroll kept a close eye upon the departures of society women for other cities. His vigil had been unrewarded thus far. And the public as a whole waited eagerly for her apprehension, for the public was unanimous in the belief that the woman in the taxicab was the person who had ended Warren's life.

The very fact of having nothing definite upon which to work was getting on Carroll's usually equable nerves. He had little to say to Leverage regarding the case, for the simple reason that there was very little which could be said. Leverage, on his part, watched the detective with keen interest, sympathizing with him, and exhibiting implicit confidence, but the men didn't agree upon the correct procedure. Leverage was all for arresting Barker and charging him with the murder.

"You'll learn some facts then, Carroll," he insisted.

But Carroll shook his head.

"It wouldn't get us anywhere, Eric. We couldn't prove him guilty."

"No-o, but that don't make no difference. Of course the law says a man is innocent until you prove he ain't, but that ain't what the law does. If we arrest this here Mr. William Barker, everybody's going to believe he's guilty until he proves himself innocent."

"And you think he can't do that?"

"No! At least I'm gambling on this—Barker can't prove himself innocent without telling who is guilty!"

But Carroll refused to arrest the man. He knew that Leverage disapproved, but he also knew that Leverage was sportsman enough to let him handle the case in his own way.

On one of his long strolls through the downtown section of the city—daily walks which helped him to think connectedly—David Carroll felt a hand on his arm and heard an eager feminine voice in his ear:

"Gracious goodness! If it isn't the perfectly marvelous Mr. David
Carroll!"

Carroll bowed instinctively. Then his lips expanded into the first wholesome smile he had experienced in forty-eight hours.

"Miss Evelyn Rogers!"

"You did recognize me, didn't you? How simply splendiferous! I'm awfully glad we met!"

"So am I, Miss Rogers."

She dropped her voice confidentially.

"Will you do me a great favor—an enormous favor?"

"Certainly. What is it?"

"It's this." She looked around carefully. "I told some of my friends that you are a friend of mine, and they don't believe it. They're over yonder in that ice-cream place. Now, what I want you to do for me is to show 'em. I want you to take me over there and buy me an ice-cream soda!"

Carroll laughed aloud as he took her by the arm and piloted her through the traffic. He asked only one question:

"What flavor?"