Although I felt discouraged on our return to the city, the morning following our exciting adventure at the mysterious house in the Ramapo valley, Garrick, who never let anything ruffle him long, seemed quite cheerful.

"Cheer up, Tom," he encouraged. "We are on the home stretch now."

"Perhaps—if they don't beat us to the tape," I answered disconsolately. "What are you going to do next?"

"While you were snatching a little sleep, I was rummaging around and found a number of letters in a table drawer, up there. One was a note, evidently to the garage keeper, and signed merely, 'Chief.' I'll wager that the handwriting is the same as that in the blackmailing letter to Miss Winslow."

"What of it?" I asked, refusing to be comforted. "We haven't got him and the prospects—"

"No, we haven't got him," interrupted Garrick, "but the note was just a line to tell the Boss, who seemed to have been up there in the country at the time, to meet the Chief at 'the Joint,' on Second Avenue."

I nodded, but before I could speak, he added, "It didn't say any more, but I think I know the place. It is the old International Cafe, a regular hang-out for crooks, where they come to gamble away the proceeds of their crimes in stuss, the great game of the East Side, now. Anyhow, we'll just drop into the place. We may not find them, but we'll have an interesting time. Then, there is the possibility of getting a strangle hold on someone, anyhow."

Garrick was evidently figuring on having driven our gunman back into the haunts of the underworld.

There seemed to be no other course that presented itself and therefore, rather than remain inactive until something new turned up, I consented to accompany him in his excursion.

Forbes, still uncommunicatively protesting that he would say nothing until he had an opportunity to consult a lawyer, had been taken down to New York by Dillon during the morning and was lodged in a West Side prison under a technical charge which was sufficient to hold him until Garrick could investigate his case and fix his real status.

We had taken a cross-town car, with the intention of looking over the dive where Garrick believed the crooks might drop in. The ride itself was uninteresting, but not so by any means the objective point of our journey.

Over on the East Side, we found the International Cafe, and slouched into the back room. It was not the room devoted to stuss, but the entrance to it, which Garrick informed me was through a heavy door concealed in a little hallway, so that its very existence would not be suspected except by the initiate.

We made no immediate attempt to get into the hang-out proper, which was a room perhaps thirty feet wide and seventy feet deep. Instead, we sat down at one of the dirty, round tables, and ordered something from the waiter, a fat and oily Muscowitz in a greasy and worn dinner coat.

It seemed that in the room where we were had gathered nearly every variety of the populous underworld. I studied the men and women at the tables curiously, without seeming to do so. But there could be no concealment here. Whatever we might be, they seemed to know that we were not of them, and they greeted us with black looks and now and then a furtive scowl.

It was not long, however, before it became evident that in some way word had been passed that we were not mere sightseers. Perhaps it was by a sort of wireless electric tension that seemed to pervade the air. At any rate, it was noticeable.

"There's no use staying here," remarked Garrick to me under his breath, affecting not to notice the scowls, "unless we do something. Are you game for trying to get into the stuss joint?"

He said it with such determination to go himself that I did not refuse. I had made up my mind that the only thing to do was to follow him, wherever he went.

Garrick rose, stretched himself, yawned as though bored, and together we lounged out into the public hall, just as someone from the outside clamoured for admission to the stuss joint through the strong door.

The door had already been opened, when Garrick deftly inserted his shoulder. Through the crack in the door, I could see the startled roomful of players of all degrees in crookdom, in the thick, curling tobacco smoke.

The man at the door called out to Garrick to get out, and raised his arm to strike. Garrick caught his fist, and slowly with his powerful grip bent it back until the man actually writhed. As his wrist went back by fractions of an inch, his fingers were forced to relax. I knew the trick. It was the scientific way to open a clenched fist. As the tendons refused to stretch any farther, his fingers straightened, and a murderous looking blackjack clattered to the floor.

All was confusion. Money which was on the various tables disappeared as if by magic. Cards were whisked away as if a ghost had taken them. In a moment there was no more evidence of gambling than is afforded by any roomful of men, so easy was it to hide the paraphernalia, or, rather, lack of paraphernalia of stuss.

It was the custom, I knew, for criminals, after they had made a haul to retire into such places as these stuss parlors, not only to spend the proceeds of their robberies, but for protection. Even though they were unmercifully fleeced by the gamblers, they might depend on them to warn of the approach of the "bulls" and if possible count on being hidden or spirited off to safety.

Apparently we had come just at a time when there were some criminals in hiding among the players. It was the only explanation I could offer of the strange action that greeted our simple attempt to gain admission to the stuss room. Whether they were criminals who had really made a haul or mere fugitives from justice, I could not guess. But that a warning had been given the man at the door to be on his guard, seemed evident from the manner in which we had been met.

There was a rush of feet in the room. I expected that we would be overwhelmed. Instead, as together we pushed on the now half-open door, the room emptied like a sieve. Whoever it might be who had taken refuge there had probably disappeared, among the first, by tacit understanding of the rest, for the whole thing had the air of being run off according to instructions.

"It's a collar!" had sounded through the room, the moment we had appeared at the door, and it was now empty.

I wondered whether the letter which Garrick had found might not, after all, have brought us straight to the last resort of those whom we sought.

"Where have they gone?" I panted, as the door opened at last, and we found only one man in the place.

There he stood apparently ready to be arrested, in fact courting it if we could show the proper authority, since he knew that it would be only a question of hours when he would be out again and the game would be resumed, in full blast.

The man shook his head blankly in answer to my question.

"There must be a trap door somewhere," cried Garrick. "It is no use to find it. They are all on the street by this time. Quick—before anyone catches us in the rear."

We had been not a moment too soon in gaining the street. Though we had done nothing but attempt to get into the stuss room, ostensibly as players, the crowd in the cafe was pressing forward.

On the street, we saw men filing quickly from a cellar, a few doors down the block. We mingled with the excited crowd in order to cover ourselves.

"That must have been where the trap door and passage led," whispered
Garrick.

A familiar figure ducked out of the cellar, surrounded by others, and the crowd made for two taxicabs standing on the opposite side of the street near a restaurant which was really not a tough joint but made a play at catering to people from uptown who wanted a taste of near-crime and did not know when they were being buncoed.

Another cab swung up to the stand, just as the first two pulled away.
Its sign was up: "Vacant."

Quick as a flash, Garrick was in it, dragging me after him. The driver must have thought that we, too, were escaping, for he needed only one order from Garrick to leap ahead in the wake of the cabs which had already started.

A moment later, Garrick's head was out of the window. He had drawn his revolver and was pegging away at the tires of the cabs ahead. An answering shot came back to us. Meanwhile, a policeman at a corner leaped on a passing trolley and urged the motorman to put on the full power in a vain effort to pursue us as we swept by up the broad avenue.

Even the East Side, accustomed to frequent running fights on the streets between rival gunmen and gangs, was roused by such an outburst. The crack of revolver shots, the honking of horns, the clang of the trolley bell, and the shouts of men along the street brought hundreds to the windows, as the cars lurched and swayed up the avenue.

The cars ahead swerved to dodge a knot of pedestrians, but their pace never slackened. Then the rearmost of the two began to buck and almost leap off the roadway. There came a rattle and roar from the rear wheels which told that the tires had been punctured and that the heavy wheels were riding on their rims, cutting the deflated tubes. At a cross street the first car turned, just in time to avoid a truck, and dodged down a maze of side streets, but the second ran squarely into the truck.

As the first car disappeared we caught a glimpse of a man leaning out of it. He seemed to be swinging something around and around at arm's length. Suddenly he let it go and it shot high up in the air on the roof of a tenement house.

"The automobile is the most dangerous weapon ever used by criminals," muttered Garrick, as the first car shot down through a mass of trucking which had backed up and shifted, making pursuit momentarily more impossible for us. "These people know how to use the automobile, too. But we've got someone here, anyhow," he cried, leaping out and pushing aside the crowd that had collected about the wrecked car.

In the bottom of it we found a man, stunned and crumpled into a heap.
Blood flowed from his arm where one of the bullets had struck him.
Several bullets had struck the back of the cab and both tires were cut
by them.

As I came up and looked over Garrick's shoulder at the prostrate and unconscious figure in the car, I could not restrain an exclamation of surprise.

It was the garage keeper, the Boss—at last!

Policemen had come up in the meantime, and several minutes were consumed while Garrick proved to them his identity.

"What was that thing the fellow in the forward car whirled over his head?" I whispered.

"A revolver, I think," returned Garrick. "That's a favourite trick of the gunmen. With a stout cord tied to a gun you can catapult it far enough to destroy the evidence that will hold you under the Sullivan law, at least. I mean to get that gun as soon as we are through with this fellow here."

Someone had turned in a call for an ambulance which came jangling up soon after, and we stood in a group close to the young surgeon as he worked to bring around the captured gangster.

"Where's the Chief?" he mumbled, dazed.

Garrick motioned to us to be quiet.

The man rambled on with a few inconsequential remarks, then opened his eyes, caught sight of the white coated surgeon working over him, of us standing behind, and of the crowd about him.

Memory of what had happened flitted back to him. With an effort he was himself again, close-mouthed, after the manner of the gangsters.

The surgeon had done all in his power and the man was sufficiently recovered to be taken to the hospital, now, under arrest. As far as we were concerned, our work was done. The Boss could be found now, at any time that we needed him, but that he would speak all the traditions of gangland made impossible.

I wondered what Garrick would do. As for myself, I had no idea what move to make.

It surprised me, therefore, to see him with a smile of satisfaction on his face.

"I'll see you this afternoon, Tom," he said merely, as the ambulance bore the wounded Boss away. "Meanwhile, I wish you'd take the time to go over to headquarters and give Dillon our version of this affair. Tell him to hold to-night open, too. I have a little work to do this afternoon, and I'll call him up later."

Dillon, I found, was overjoyed when I reported to him the capture of at least one man whom we had failed to get the night before.

"Things seem to be clearing up, after all," he remarked. "Tell Garrick I shall hold open to-night for him. Meanwhile, good luck, and let me know the moment you get any word about the Chief. He must have been in. that first cab, all right."

As I left Dillon's office, I ran into Herman in the hall, coming in. I bowed to him and he nodded surlily. Evidently, I thought, he had heard of the result of our activities. I did not ask him what progress he had made in the case, for I had had experience with professional jealousy before, and thought that the less said on the subject the better.

Recalling what Garrick had said, I curbed my impatience as best I could, in order to give him ample time to complete the work that he had to do. It was not until the middle of the afternoon that I rejoined him in his office.

I found him at work at a table, still, with a microscope and an arrangement which I recognised as the apparatus for making microphotographs. Several cartridges, carefully labelled, were lying before him, as well as the peculiar pistol we had found when we had captured Forbes in the little room. There were also the guns we had captured in the garage and one found in the cab which we had chased and wrecked.

On the end of the table was a large number of photographs of a most peculiar nature. I picked up one. It looked like an enlarged photograph of an orange, or like some of the pictures which the astronomers make of the nearer planets.

"What are these?" I asked curiously, as he leaned back from his work, with a smile of quiet satisfaction.

"That is a collection of microphotographs which I have gathered," he answered, adding, "as well as some that I have just made. I hope to use them in a little stereopticon entertainment I am arranging to-night for those who have been interested in the case."

Garrick smiled. "Have you ever heard?" he asked, "that the rounded end of the firing pin of every rifle when it is examined under a microscope bears certain irregularities of marking different from those of every other firing pin and that the primer of every shell fired in a rifle is impressed with the particular markings of that firing pin?"

I had not, but Garrick went on, "I know that it is true. Such markings are distinctive for each rifle and can be made by no other. I have taken rifles bearing numbers preceding and following that of a particular one, as well as a large number of other firing pins. I have tried the rifles and the firing pins, one by one, and after I made microphotographs of the firing pins with special reference to the rounded ends and also photographs of the corresponding rounded depressions in the primers fired by them, it was forced upon me that cartridges fired by each individual firing pin could be positively identified."

I had been studying the photographs. It was a new idea, and it appealed to me strongly. "How about revolvers?" I asked quickly.

"Well, Dr. Balthazard, the French criminologist, has made experiments on the identification of revolver bullets and has a system that might be compared to that of Bertillon for identifying human beings. He has showed by greatly enlarged photographs that every gun barrel leaves marks on a bullet and that the marks are always the same for the same barrel but never identical for two different barrels. He has shown that the hammer of a revolver, say a centre fire, strikes the cartridge at a point which is never the exact centre of the cartridge, but is always the same for the same weapon. He has made negatives of bullets nearly a foot wide. Every detail appears very distinctly and it can be decided with absolute certainty whether a certain bullet or cartridge was fired by a certain revolver."

He had picked up one of the microphotographs and was looking at it attentively through a small glass.

"You will see," he explained, "on the edge of this photograph a rough sketch calling attention to a mark like an L which is the chief characteristic of this hammer, although there are other detailed markings which show well under the microscope but not in a photograph. You will note that the marks on a hammer are reversed on the primer in the same way that a metal type and the character printed by it are reversed as regards one another. Moreover, depressions on the end of a hammer become raised on the primer and raised markings on the hammer become depressions on the primer.

"Now, here is another. You can see that it is radically different from the first, which was from the cartridge used in killing poor Rena Taylor. This second one is from that gun which I found on the tenement roof this morning. It lacks the L mark as well as the concentric circles. Here is another. Its chief characteristics are a series of pits and elevations which, examined under the microscope and measured, will be found to afford a set of characters utterly different from those of any other hammer.

"In short," he concluded with an air of triumph, "the ends of firing pins are turned and finished in a lathe by the use of tools designed for that purpose. The metal tears and works unevenly so that microscopical examination shows many pits, lines, circles, and irregularities. The laws of chance are as much against two of these firing pins or hammers having the same appearance under the microscope as they are against the thumb prints of two human subjects being identical."

I picked up the curious little arrangement which we had found in the drawer in Forbes' room and examined it closely.

"I have been practicing with that pistol, if you may call it that," he remarked, "on cartridges of my own and examining the marks made by the peculiar hammer. I have studied marks of the gun which we found on the roof. I have compared them with the marks on cartridges which we have picked up at the finding of Rena Taylor's body, at the garage that night of the stupefying bullet, with bullets such as were aimed at Warrington, with others, both cartridges and bullets, at various times, and the conclusion is unescapable."

Who, I asked myself, was the scientific gunman? I knew it was useless to try to hurry Garrick. First, by a sort of intuition he had picked him out, then by the evidence of hammer and bullet he had made it practically certain. But I knew that to his scientific mind nothing but absolute certainty would suffice.

While I was waiting for him to proceed, he had already begun to work on some apparatus behind a screen at the end of his office. Close to the wall at the left was a stereopticon which, as nearly as I could make out, shot a beam of light through a tube to a galvanometer about three feet distant. In front of this beam whirled a five-spindled wheel governed by a chronometer which was so accurate, he said, that it erred only a second a day.

Between the poles of the galvanometer was stretched a slender thread of fused quartz plated with silver. It was the finest thread I could imagine, only a thousandth of a millimeter in diameter, far too tenuous to be seen. Three feet further away was a camera with a moving plate holder which carried a sensitized photographic plate. Its movement was regulated by a big fly-wheel at the extreme right.

"You see," remarked Garrick, now engrossed on the apparatus and forgetting the hammer evidence for the time, "the beam of light focussed on that fine thread in the galvanometer passes to this photographic plate. It is intercepted by the five spindles of the wheel, which turns once a second, thus marking the picture off in exact fifths of a second. The vibrations of the thread are enormously magnified on the plate by a lens and produce a series of wavy or zigzag lines. I have shielded the sensitized plate by a wooden hood which permits no light to strike it except the slender ray that is doing the work. The plate moves across the field slowly, its speed regulated by the fly-wheel. Don't you think it is neat and delicate? All these movements are produced by one of the finest little electric motors I ever saw."

I could not get the idea of the revolvers out of my head so quickly. I agreed with him, but all I could find to say was, "Do you think there was more than this one whom they call the Chief engaged in the shootings?"

"I can't say absolutely anything more than I have told you, yet," he answered in a tone that seemed to discourage further questioning along that line.

He continued to work on the delicate apparatus with its thread stretched between the stationary magnets of the galvanometer, a thread so delicate that it might have been spun by a microscopic spider, so light that no scales made by human hands could weigh it, so slender that the mind could hardly grasp it. It was about one-third the diameter of a red corpuscle of blood and its weight had been estimated as about .00685 milligrams, truly a fairy thread. It was finer than the most delicate cobweb and could be seen with the naked eye only when a strong light was thrown on it so as to catch the reflection.

"All I can say is," he admitted, "that the bullets which committed this horrible series of crimes have been proven all to be shot from the same gun, presumably, I think I shall show, by the same hand, and that hand is the same that wrote the blackmailing letter."

"Whose gun was it?" I asked. "Was there a way to connect it and the bullets and the cartridges with the owner—four things, all separated—and then that owner with the curious and tragic succession of events that had marked the case since the theft of Warrington's car?"

Garrick had apparently completed his present work of adjusting the delicate apparatus. He was now engaged on another piece which also had a powerful light in it and an attachment which bore a strong resemblance to a horn.

He paused a moment, regarding me quizzically. "I think you'll find it sufficiently novel to warrant your coming, Tom," he added. "I have already invited Dillon and his man, Herman, over the telephone just before you came in. McBirney will be there, and Forbes, of course. He'll have to come, if I want him. By the way, I wish you'd get in touch with Warrington and see how he is. If it is all right, tell him that I'd like to have him escort Miss Winslow and her aunt here, to-night. Meanwhile I shall find out how our friend the Boss is getting on. He ought to be here, at any cost, and I've put it off until to-night to make sure that he'll be in fit condition to come. To-night at nine—here in this office—remember," he concluded gayly. "In the meantime, not a word to anybody about what you have seen here this afternoon."