Late that night Markham and Heath and I were sitting with Vance on his roof-garden, drinking champagne and smoking.

    We had remained at the Stamm estate only a short time after Stamm's death. Heath had stayed on to supervise the detail work which closed the case. The pool had been drained again, and Stamm's body had been taken from beneath the rock boulder. It was mutilated beyond recognition. Leland, with Miss Stamm's assistance, had taken charge of all the domestic affairs.

    Vance and Markham and I had not finished dinner until nearly ten o'clock, and shortly afterward Sergeant Heath joined us. It was still hot and sultry, and Vance had produced a bottle of his 1904 Pol Roger.

    "An amazin' crime," he remarked, lying back lethargically in his chair. "Amazin'—and yet simple and rational."

    "That may be true," Markham returned. "But there are many details of it which are still obscure to me."

    "Once its basic scheme is clear," Vance said, "the various shapes and colors of the mosaic take their places almost automatically."

    He emptied his glass of champagne.

    "It was easy enough for Stamm to plan and execute the first murder. He brought together a house-party of warring elements, on any member of which suspicion might fall if criminality were proved in connection with Montague's disappearance. He felt sure his guests would go swimming in the pool and that Montague, with his colossal vanity, would take the first dive. He deliberately encouraged the heavy drinking, and he himself pretended to overindulge. But as a matter of fact, he was the only member of the party, with the possible exception of Leland and Miss Stamm, who did no drinking."

    "But Vance—"

    "Oh, I know. He gave the appearance of having drunk heavily all day. But that was only part of his plan. He was probably never more sober in his life than when the rest of the party left the house for the swimming pool. During the entire evening he sat on the davenport in the library, and surreptitiously poured his liquor into the jardinière holding the rubber-plant."

    Markham looked up quickly.

    "That was why you were so interested in the soil of that plant?"

    "Exactly. Stamm had probably emptied two quarts of whisky into the pot. I took up a good bit of the soil on my finger; and it was well saturated with alcohol."

    "But Doctor Holliday's report—"

    "Oh, Stamm was actually in a state of acute alcoholism when the doctor examined him. You remember the quart of Scotch he ordered from Trainor, just before the others went down to the pool. When he himself came back to the library, after the murder, he undoubtedly drank the entire bottle; and when Leland found him his state of alcoholic collapse was quite genuine. Thus he gave the whole affair an air of verisimilitude."

    Vance lifted the champagne from the wine cooler and poured himself another glass. When he had taken a few sips he lay back again in his chair.

    "What Stamm did," he continued, "was to hide his diving outfit and the grapnel in his car in the garage earlier in the day. Then, feigning a state of almost complete drunken insensibility, he waited till every one had gone to the pool. Immediately he went to the garage, and drove—or perhaps coasted—down the East Road to the little cement path. He donned his diving suit, which he put on over his dinner clothes, and attached the oxygen tank—a matter of but a few minutes. Then he put the board in place, and entered the pool. He was reasonably sure that Montague would take the first dive; and he was able to select almost the exact spot in the pool toward which Montague would head. He had his grapnel with him, so that he could reach out in any direction and get his victim. The water in the pool is quite clear and the flood-lights would give him a good view of Montague. The technique of the crime for an experienced diver like Stamm was dashed simple."

    Vance made a slight gesture with his hand.

    "There can be little doubt as to exactly what happened. Montague took his dive, and Stamm, standing on the sloping basin opposite the deep channel, simply hooked him with the grappling-iron—which accounts for the wounds on Montague's chest. The force of the dive, I imagine, drove Montague's head violently against the metal oxygen tank clamped to the breast-plate of Stamm's helmet, and fractured his skull. With his victim stunned and perhaps unconscious, Stamm proceeded to choke him under the water until he was quite limp. It was no great effort for Stamm to drag him to the car and throw him in. Next Stamm replaced the board, doffed his diving suit, hid it in the old coffin in the vault, and drove to the pot-holes, where he dumped Montague's body. Montague's broken bones were the result of the rough way in which Stamm chucked him into the rock pit; and the abrasions on his feet were undoubtedly caused by Stamm's dragging him over the cement walk to the parked car. Afterward Stamm drove the car back to the garage, returned cautiously to the library, and proceeded to consume the quart of whisky."

    Vance took a long inhalation on his cigarette, exhaling the smoke slowly.

    "It was an almost perfect alibi."

    "But the time element, Vance—" Markham began.

    "Stamm had plenty of time. At least fifteen minutes elapsed before the others had changed to their bathing suits; and this was twice as much time as Stamm required to coast down the hill in his car, slip into his diving suit, put the piece of lumber in place, and station himself in the pool. And, certainly, it took him not more than fifteen minutes, at the most, to replace the board, hide his diving suit, deposit his victim in the pot-hole, and return to the house."

    "But he was taking a desperate chance," Markham commented.

    "On the contr'ry, he was taking no chance at all. If his calculations worked out successfully, there was no way in which the plot could go awry. Stamm had all the time necess'ry; he had the equipment; and he was working out of sight of any possible witnesses. If Montague had not dived into the pool, as was his custom, it would have meant only that the murder would have to be postponed. In that case Stamm would simply have walked out of the pool, returned to the house, and bided his time."

    Vance frowned wistfully and turned his head lazily toward Markham.

    "There was, however, one fatal error in the calculations," he said. "Stamm was too cautious—he lacked boldness: he covered his gamble, as it were. As I have said, in planning the house-party he invited persons who had reason to want Montague out of the way, his idea being to supply the authorities with suspects in the event his scheme did not work out. But, in doing so, he overlooked the fact that some of these very people were familiar with diving apparatus and with his own under-sea work in the tropics—people who, having this information, might have figured out how the murder was committed, provided the body was found. . . ."

    "You mean," asked Markham, "that you think Leland saw through the plot from the first?"

    "There can be little doubt," Vance returned, "that when Montague failed to come up from his dive, Leland strongly suspected that Stamm had committed a crime. Naturally, he was torn between his sense of justice and fair play, on the one hand, and his love for Bernice Stamm, on the other. My word, what a predicament! He compromised by telephoning to the Homicide Bureau and insisting that an investigation be instigated. He wouldn't definitely expose or accuse the brother of the woman he loved. But, as an honorable man, he couldn't bring himself to countenance what he believed to be deliberate murder. Y' know, Markham, he was infinitely relieved when I told him this afternoon that I knew the truth. But meanwhile the man had suffered no end."

    "Do you think any one else suspected?" Markham asked.

    "Oh, yes. Bernice Stamm suspected the truth—Leland himself told us so this afternoon. That's why the Sergeant, when he first saw her, got the impression she was not primarily worried about Montague's disappearance.—And I feel pretty sure that Tatum also guessed the truth. Don't forget, he had been on the trip to Cocos Island with Stamm and was familiar with the possibilities of diving suits. But the present situation no doubt seemed a bit fantastic to him, and he couldn't voice his suspicion because there was apparently no way of proving it.—And Greeff, too, having helped to equip some of Stamm's expeditions, undoubtedly had a fairly accurate idea as to what had happened to Montague."

    "And the others also?" asked Markham.

    "No, I doubt if either Mrs. McAdam or Ruby Steele really suspected the truth; but I think both of them felt that something was wrong. Ruby Steele was attracted by Montague—which accounts, perversely, for the antagonism between them. And she was jealous of Bernice Stamm as well as of Teeny McAdam. When Montague disappeared, I have no doubt the idea of foul play did enter her mind. That's why she accused Leland: she hated him because of his superiority."

    Vance paused a moment and went on.

    "Mrs. McAdam's mental reactions in the matter were a bit subtler. I doubt if she entirely understood her own emotions. Unquestionably, however, she too suspected foul play. Although the fact that Montague had faded from the scene would have favored her personal ends, I imagine she had some lingerin' sentiment for the chap, and that's why she handed us Greeff and Leland as possibilities—both of whom she disliked. And I imagine also that her scream was purely emotional, while her later indifference indicated the dominance of her scheming mind over her heart. The horror of the possibility of Montague's having been murdered accounted for her violent reaction when I told her of the splash in the pool: she pictured terrible things happening to him. The old feminine heart at work again, Markham."

    There were several moments of silence. Then Markham said, almost inaudibly, as if stating to himself some point in a train of thought:

    "And of course the car that Leland and Greeff and Miss Stamm heard was Stamm's."

    "Unquestionably," Vance returned. "The time element fitted exactly."

    Markham nodded, but there was a troubled reservation in his frown.

    "But still," he said, "there was that note from the Bruett woman."

    "My dear Markham! There's no such person. Stamm created Ellen Bruett to account for Montague's disappearance. He was hoping that the whole affair would simply blow over as a commonplace elopement. He wrote the rendezvous note himself, and put it in Montague's pocket after he returned from the pool that night. And you remember that he indicated where we could find it, when he opened the clothes-closet door. A clever ruse, Markham; and the sound of the car on the East Road bore out the theory, though Stamm probably didn't take the sound of the car into consideration at all."

    "No wonder my men couldn't find any trace of the dame," grumbled the Sergeant.

    Markham was gazing at his cigar with a thoughtful abstracted look.

    "I can understand the Bruett factor," he remarked at length; "but how do you account for Mrs. Stamm's uncannily accurate prophecies?"

    Vance smiled mildly.

    "They were not prophecies, Markham," he replied, with a sad note in his voice. "They were all based on real knowledge of what was going on, and were the pathetic attempts of an old woman to protect her son. What Mrs. Stamm didn't actually see from her window, she probably suspected; and nearly everything she said to us was deliberately calculated to divert us from the truth. That's why she sent for us at the outset."

    Vance drew deeply on his cigarette again, and looked out wistfully over the tree-tops.

    "Much of her talk about the dragon was insincere, although there is no question that the hallucination concerning the dragon in the pool had taken a powerful hold on her weakened mind. And this partial belief in the existence of a water-monster formed the basis of her defense of Stamm. We don't know how much she saw from her window. Personally, I think she felt instinctively that Stamm had plotted the murder of Montague, and I also think that she heard the car going down the East Road and suspected what its errand was. When she listened at the top of the stairs that first night and heard Stamm protesting, the shock produced by the realization of her fears caused her to scream and to send for us later to tell us that no one in the house was guilty of any crime."

    Vance sighed.

    "It was a tragic effort, Markham; and all her other efforts to mislead us were equally tragic. She attempted to build up the dragon hypothesis because she herself was not quite rational on the subject. Moreover, she knew Stamm would take the body away and hide it—which accounts for her seeming prophecy that the body would not be found in the pool. And she was able to figure out where Stamm would hide the body—in fact, she may even have been able to tell, from the sound, approximately how far down the road Stamm drove the car before returning to the garage. When she screamed at the time the pool was emptied, she was simply making a dramatic gesture to emphasize her theory that the dragon had flown off with Montague's body."

    Vance stretched his legs and settled even deeper into his chair.

    "Mrs. Stamm's prognostications of the second tragedy were merely another effort toward foisting the dragon theory upon us. She undoubtedly suspected that her son, having succeeded in murdering Montague, would, if the opportunity presented itself, also put Greeff out of the way. I imagine she knew all about Greeff's financial plottings, and sensed Stamm's hatred for him. She may even have seen, or heard, her son and Greeff go down toward the pool last night and have anticipated the terrible thing that was going to happen. You recall how frantically she endeavored to bolster up her theory of the dragon when she heard of Greeff's disappearance. I had a suspicion then that she knew more than she would admit. That was why I went directly to the potholes to see if Greeff's body was there. . . . Oh, yes, that tortured old woman knew of her son's guilt. When she begged Leland to bring him back into the house this afternoon, saying that some danger was lurking in the pool, it wasn't a premonition. It was only her instinctive fear that some retribution might overtake her son at the scene of his crimes."

    "And it did overtake him," mumbled Markham. "A curious coincidence."

    "He sure had it coming to him," put in the practical Sergeant. "But what gets me is the trouble he took to avoid leaving footprints."

    "Stamm had to protect himself, Sergeant," Vance explained. "Any noticeable imprints of his diving shoes would have given away the entire plot. Therefore, he took the precaution of placing a board over that patch of ground."

    "But he took no precaution against his footprints on the bottom of the pool," Markham submitted.

    "True," Vance returned. "It had not occurred to him, I imagine, that the imprints he made under the water would remain; for he was certainly a frightened man when the marks of his diving shoes came to light: he was afraid they would be recognized for what they were. I admit that the truth did not occur to me at the time. But, later, a suspicion of the truth dawned on me; and that is why I wished to verify my theory by searching for a diving suit and shoes and gloves. There are but few companies that make standard diving equipment in this country, and I had little trouble in locating the firm from which Stamm had acquired his outfit."

    "But what about Leland?" Markham asked. "Surely he would have recognized the tracks."

    "Oh, to be sure. In fact, the moment I mentioned those strange tracks to him, he suspected immediately how they had been made; and when he saw Snitkin's drawings he knew the truth. I think he rather hoped that we also would see it, although he could not bring himself to tell us directly because of his loyalty to Bernice Stamm. Miss Stamm herself suspected the truth—you recall how upset she was when I mentioned the queer footprints to her. And Mrs. Stamm, too, knew the significance of those imprints when she heard of them. But she very cleverly turned them to her own purpose and used them to support the theory of the dragon that she was endeavorin' to instil in us."

    Markham filled his glass.

    "That part of it is all clear," he said, after a short silence. "But there are certain points connected with Greeff's murder that I don't yet understand."

    Vance did not speak at once. First he lighted a fresh cigarette slowly and meditatively. Then he said:

    "I can't make up my mind, Markham, whether Greeff's murder was planned for this particular week-end, or was suddenly decided on. But the possibility unquestionably was at the back of Stamm's mind when he planned the party. There can be no doubt that he detested Greeff and also feared him; and, with his perverted mind, he saw no way of eliminating the menace presented by Greeff except through murder. What led Stamm to his decision to do away with Greeff last night was undoubtedly the amazin' amount of dragon talk that followed the finding of the imprints on the bottom of the pool, and the claw-like tears down Montague's chest. He saw no reason why he should not continue to build up this outlandish theory of the dragon. As long as the circumstances of Montague's death appeared entirely irrational and fantastic, Stamm, no doubt, felt safe from apprehension; and in this state of false security, he sought to repeat the irrationality of Montague's death in Greeff's murder. He argued, I imagine, that if he were safe from suspicion as a result of the dragonish implications in Montague's murder, he would be equally safe from suspicion if Greeff were disposed of in a similar manner. That's why he duplicated the technique so carefully. He struck Greeff over the head to make a wound similar to the one on Montague. He then strangled Greeff, in order to reproduce the throat marks; and, that accomplished, he used the grapnel on Greeff's chest, thus reproducing the supposed dragon's claw-marks. He then carried the murder to its logical extreme—or, rather, to its reductio ad absurdum—by chucking the fellow into the pot-hole."

    "I can see how his mind was working," Markham admitted. "But in Greeff's case he had to create the opportunity for the crime."

    "Quite so. But that wasn't difficult. After Stamm's vicious outburst Saturday night, Greeff was only too glad to accept the reconciliation Stamm offered him last night in the library. You recall that Leland told us they sat for hours talking amicably before retiring. What they probably talked about was the prospect of a new expedition, and Greeff was delighted to be able to offer his help. Then, when they had gone up-stairs, Stamm undoubtedly invited Greeff into his own room for a last drink, later suggesting that they go for a walk to continue the discussion; and the two went out together. It was at that time that both Leland and Trainor heard the side door being unbolted."

    Vance again sipped his champagne.

    "How Stamm inveigled Greeff into the vault is something we'll never know. However, it's a point of no importance, for certainly Greeff was in a frame of mind to acquiesce in any suggestion Stamm might have made. Stamm may have told Greeff that he was able to explain Montague's death if the other would go into the vault with him. Or, it may have been a more commonplace invitation—the expression of a desire to inspect the masonry after the heavy rains. But whatever the means used by Stamm, we know that Greeff did enter the vault with him last night. . . ."

    "The gardenia, of course—and the bloodstains," Markham murmured.

    "Oh, yes; it was quite evident. . . . And after Stamm had killed Greeff and mutilated him exactly as he had mutilated Montague, he took him down to the pot-holes in the wheelbarrow, over the sandy ground along the foot of the cliff, where he would not attract the attention of any guard that might have been stationed on the East Road."

    Heath gave a gratified grunt.

    "And then he left the wheelbarrow in that bunch of trees, and pussy-footed back to the house."

    "Exactly, Sergeant. Moreover, the grating metallic noise that Leland heard was obviously the creaking of the rusty hinges of the vault door; and the other sound which Leland described could have been nothing but the wheelbarrow. And, despite all Stamm's caution on re-entering the house, both Leland and Trainor heard him throw the bolt."

    Vance sighed.

    "It was not a perfect murder, Markham, but it had the elements of perfection in it. It was a bold murder, too; for if either of the murders were solved, both would be solved. It was a double gamble—the placing of two chips, instead of one, on a selected number."

    Again Markham nodded sombrely.

    "That part is clear enough now," he said. "But why should the key to the vault have been found in Tatum's room?"

    "That was part of Stamm's fundamental mistake. As I have said, Stamm was overcautious. He didn't have the courage to carry through his plot without building bridges. He may have had the key for years, or he may have secured it recently from Mrs. Stamm's trunk. But really, it doesn't matter. Once he had used it for his purpose, he could not throw it away, for obviously he intended to remove the diving suit from the vault when the first opportunity offered. He could have hidden the key in the meantime; but if the diving suit had been discovered in the vault by some one's tearing down a wall or breaking in the door, suspicion would immediately have fallen on him, as it was his own diving suit. Therefore, in an effort to protect himself in this remote eventuality, he probably put the key first in Greeff's room, to point suspicion to Greeff. Then, when the opportunity to murder Greeff arose, Stamm planted the key in Tatum's room. Stamm liked Leland and wanted Bernice to marry him—which, incidentally, was the primary motive for his getting rid of Montague—and he certainly would not have tried to throw suspicion on Leland. You will remember that I first searched Greeff's room—I thought that the key might be there, inasmuch as there was a possibility we would think that Greeff had merely run away. But when it was not there I looked for it in Tatum's room. Luckily we found it and didn't have to break into the vault—which I would certainly have insisted upon if there had been no other means of entering."

    "But what I still don't understand, Vance," Markham persisted, "is why the key should have interested you in the first place."

    "Neither do I—entirely," Vance returned. "And it's much too hot tonight to indulge in psychological analyses of my mental quirks. Let's say, for brevity, that my idea about the key was mere guesswork. As you know, the vault fascinated me because of its strategic position; and I couldn't see how else the first murder could have been so neatly accomplished unless the vault had been used in some way. It was most convenient, don't y' know. But the entire matter was far from clear in my mind. In fact, it was dashed vague. However, I thought it worth determining, and that's why I went to Mrs. Stamm and demanded to know the hiding-place of the key. I frightened her into telling me, for she didn't associate the vault with Stamm's machinations. When I discovered that the key had disappeared from its hiding-place, I was more convinced than ever that it was a factor in the solution of our problem."

    "But how, in the name of Heaven," asked Markham, "did you first hit upon the idea that Stamm was the guilty person? He was the only person in the house that seemed to have a good alibi."

    Vance shook his head slowly.

    "No, Markham old dear; he was the only member of the party who did not have an alibi. And it was for that reason that I had my eye on him from the first—although I admit there were other possibilities. Stamm, of course, thought that he had built up a perfect alibi, at the same time hoping that the murder would pass as a mere departure. But when Montague's murder was established, Stamm's position was really weaker than that of any of the others; for he was the only one who was not standing beside the pool at the time Montague dived in. It would have been difficult for any one of the others to have murdered Montague in the circumstances, just as it would have been impossible for Stamm to have murdered him if he had actually been in a state of acute alcoholism. It was this combination of circumstances that gave me my first inkling of the truth. Naturally, Stamm couldn't have gone to the pool with the others and still have accomplished his purpose; and, reasoning from this premise, I arrived at the conclusion that it was possible for him to have feigned drunkenness by secretly disposing of his liquor, and then made his drunkenness a reality after he had returned to the house. When I learned that he had spent the entire evening on the davenport in the library, I naturally became interested in the jardinière holding the rubber-plant at the head of the davenport."

    "But, Vance," protested Markham, "if you were so certain from the first that the crime was rational and commonplace, why all the silly pother about a dragon?"

    "It was not silly. There was always the remote possibility that some strange fish, or sea-monster, had been responsible for Montague's death. Even the greatest zoologists understand but little about aquatic life: it is positively amazin' how meagre our knowledge of under-water creatures really is. The breeding of the Betta, for instance, has been going on for decades, and with all our experimentation with this labyrinth family, no one knows whether the Betta pugnax is a nest-builder or a mouthbreeder. Mrs. Stamm was quite right when she ridiculed scientific knowledge of submarine life. And you must not forget, Markham, that Stamm was an ardent fish hunter, and that he brought back to this country all kinds of rare specimens about which practically nothing is known. Scientifically, the superstition of the pool could not be ignored. But, I admit, I did not take the matter very seriously. I clung childishly to the trodden paths, for life has a most disappointin' way of proving commonplace and rational when we are hopin' most passionately for the bizarre and supernatural. Anyway, I thought it worth while to inspect Stamm's collection of fish. But I was more or less familiar with all his exhibits; so I descended to the realm of simple, understandable things, and tested the soil in the jardinière."

    "And incidentally," Markham commented, with a slow smile, "you lingered over the fish and the other plants so as not to give Stamm any idea of what you were really after in the rubber-plant pot."

    Vance smiled back.

    "It may be, don't y' know. . . . How about another magnum of Pol Roger?" And he rang for Currie.

    It was less than a year after these two sinister murders at the old Dragon Pool, with their sequence of tragedies, that Leland and Bernice Stamm were married. They were both strong and, in many ways, remarkable characters; but the memory of the tragedies affected them too deeply for them to remain in Inwood. They built a home in the hills of Westchester, and went there to live. Vance and I visited them shortly after their marriage.

    The old Stamm residence was never occupied again, and the estate was acquired by the city and added to what is now Inwood Hill Park. The house was torn down, and only the crumbling stones of its foundation remain. But the two square stone posts of the entrance gate, which marked the beginning of the driveway from Bolton Road, are still standing. The old Dragon Pool exists no more. The stream that fed it was diverted into Spuyten Duyvil Creek. Its semi-artificial bed has been filled in, and what was once the basin of the Dragon Pool is now overgrown with wild vegetation. It would be difficult today even to trace the course of the old stream or to determine the former boundaries of that sinister and tragic pool.

    After the final tragedy and the breaking up of the century-old traditions of the Stamm estate, I often wondered what became of Trainor, the butler, when the doors of the ancient mansion had been closed for all time. Why the memory of the fellow should have remained in my mind, I cannot say; but there was in him something at once ghost-like and corporeal, something both pathetic and offensive, which made a strong impression on me. I was, therefore, glad when I recently ran into him.

    Vance and I were visiting a tropical-fish shop in East 34th Street; and there, behind the counter, half hidden by the tanks, was Trainor.

    He recognized Vance at once, and shook his head lugubriously as we approached him.

    "I'm not doing so well with my Scatophagus here," he repined. "Not the proper conditions—if you know what I mean, sir."