At half-past nine the following day Vance drove to Markham's quarters to take him back to the old Stamm estate in Inwood. On the way home the night before, Markham had protested mildly against continuing the case before the Medical Examiner had made his report; but his arguments were of no avail. So determined was Vance to return to the house next day, that Markham was impressed. His long association with Vance had taught him that Vance never made such demands without good reason.

    Vance possessed what is commonly called an intuitive mind, but it was, in fact, a coldly logical one, and his decisions, which often seemed intuitive, were in reality based on his profound knowledge of the intricacies and subtleties of human nature. In the early stages of any investigation he was always reluctant to tell Markham all that he suspected: he preferred to wait until he had the facts in hand. Markham, understanding this trait in him, abided by his unexplained decisions; and these decisions had rarely, to my knowledge, proved incorrect, founded, as they were, on definite indications which had not been apparent to the rest of us. It was because of Markham's past experiences with Vance that he had grudgingly, but none the less definitely, agreed to accompany him to the scene of the tragedy the following morning.

    Before we left the Stamm house the night before, there had been a brief consultation with Heath, and a course of action had been mapped out under Vance's direction. Every one in the house was to remain indoors; but no other restrictions were to be placed upon their actions. Vance had insisted that no one be allowed to walk through the grounds of the estate until he himself had made an examination of them; and he was particularly insistent that every means of access to the pool be kept entirely free of people until he had completed his inspection. He was most interested, he said, in the small patch of low ground north of the filter, where Heath and Hennessey had already looked for footprints.

    Doctor Holliday was to be permitted to come and go as he chose, but Vance suggested that the nurse whom the doctor had called in be confined to the house, like the others, until such time as she was given permission to depart. Trainor was ordered to instruct the other servants—of whom there were only two, a cook and a maid—that they were to remain indoors until further notice.

    Vance also suggested that the Sergeant place several of his men around the house at vantage points where they could see that all orders were carried out by the guests and members of the household. The Sergeant was to arrange for a small corps of men to report at the estate early the following morning to close the gates above the filter and open the lock in the dam, in order that the pool might be drained.

    "And you'd better see that they come down the stream from the East Road, Sergeant," Vance advised, "so there won't be any new footprints round the pool."

    Heath was placed in complete charge of the case by Markham, who promised to get the official verification of the assignment from Commanding Officer Moran of the Detective Bureau.

    Heath decided to remain at the house that night. I had never seen him in so eager a frame of mind. He admitted frankly that he could see no logic in the situation; but, with a stubbornness which verged on fanaticism, he maintained that he knew something was vitally wrong.

    I was also somewhat astonished at Vance's intense interest in the case. Heretofore he had taken Markham's criminal investigations with a certain nonchalance. But there was no indifference in his attitude in the present instance. That Montague's disappearance held a fascination for him was evident. This was owing, no doubt, to the fact that he had seen, or sensed, certain elements in the affair not apparent to the rest of us. That his attitude was justified is a matter of public record, for the sinister horror of Montague's death became a national sensation; and Markham, with that generosity so characteristic of him, was the first to admit that, if it had not been for Vance's persistence that first night, one of the shrewdest and most resourceful murderers of modern times would have escaped justice.

    Although it was long past three in the morning when we arrived home, Vance seemed loath to go to bed. He sat down at the piano and played that melancholy yet sublime and passionate third movement from Beethoven's Sonata, Opus 106; and I knew that not only was he troubled, but that some deep unresolved intellectual problem had taken possession of his mind. When he had come to the final major chord he swung round on the piano bench.

    "Why don't you go to bed, Van?" he asked somewhat abstractedly. "We have a long, hard day ahead of us. I've a bit of reading to do before I turn in." He poured himself some brandy and soda and, taking the glass with him, went into the library.

    For some reason I was too nervous to try to sleep. I picked up a copy of "Marius the Epicurean," which was lying on the centre-table, and sat down at the open window. Over an hour later, on my way to my room, I looked in at the library door, and there sat Vance, his head in his hands, absorbed in a large quarto volume which lay on the table before him. A score of books, some of them open, were piled haphazardly about him, and on the stand at his side was a sheaf of yellowed maps.

    He had heard me at the door, for he said: "Fetch the Napoleon and soda, will you, Van? There's a good fellow."

    As I placed the bottles in front of him I looked over his shoulder. The book he was reading was an old illuminated copy of "Malleus Maleficarum." At one side, opened, lay Elliot Smith's "The Evolution of the Dragon" and Remy's "Demonolatry." At his other side was a volume of Howey's work on ophiolatry.

    "Mythology is a fascinatin' subject, Van," he remarked. "And many thanks for the cognac." He buried himself in his reading again; and I went to bed.

    Vance was up before I was the next morning. I found him in the living-room, dressed in a tan silk poplin suit, sipping his matutinal Turkish coffee and smoking a Régie.

    "You'd better ring for Currie," he greeted me, "and order your plebeian breakfast. We're picking up the reluctant District Attorney in half an hour."

    We had to wait nearly twenty minutes in Vance's car before Markham joined us. He was in execrable mood, and his greeting to us, as he stepped into the tonneau, was barely amiable.

    "The more I think of this affair, Vance," he complained, "the more I'm convinced that you're wasting your time and mine."

    "What else have you to do today?" Vance asked dulcetly.

    "Sleep, for one thing—after your having kept me up most of the night. I was slumbering quite peacefully when the hall boy rang my phone and told me that you were waiting for me."

    "Sad . . . sad." Vance wagged his head in mock commiseration. "By Jove, I do hope you sha'n't be disappointed."

    Markham grunted and lapsed into silence; and little more was said during our ride to the Stamm estate. As we drove up the circular roadway and came to a halt in the parking-space in front of the house, Heath, who had evidently been waiting for us, came down the stairs to meet us. He seemed disgruntled and ill at ease, and I noticed also that there was a skepticism and insecurity in his manner, as if he distrusted his suspicions of the night before.

    "Things are moving," he reported half-heartedly; "but nothing's happened yet. Everything is going smoothly indoors, and the whole outfit is acting like human beings for a change. They all had breakfast together, like a lot of turtle-doves."

    "That's interestin'," Vance remarked. "What about Stamm?"

    "He's up and about. Looks a little green around the gills; but he's already taken two or three eye-openers."

    "Has Miss Stamm put in an appearance this morning?"

    "Yes." Heath looked puzzled. "But there's something queer about that dame. She was having hysterics last night and fainting in every open space; but this morning she's bright and snappy, and—if you ask me—she seems relieved that her boy-friend is out of the way."

    "On whom did she lavish her attentions this morning, Sergeant?" Vance asked.

    "How should I know?" returned Heath, in an injured tone. "They didn't ask me to eat at the table with 'em—I was lucky to get any groceries at all. . . . But I noticed that after breakfast she and Leland went into the drawing-room alone and had a long palaver."

    "Really now." Vance meditated a moment, regarding his cigarette critically. "Very illuminatin'."

    "Well, well," snorted Markham, giving Vance a disdainful look. "I suppose you regard that fact as an indication that your plot is thickening?"

    Vance looked up facetiously.

    "Thickening? My dear Markham! The plot is positively congealin', not to say stiffenin'." He sobered and turned back to Heath. "Any news from Mrs. Stamm?"

    "She's all right today. The doctor was here a little while ago. He looked over the situation and said there was no more need of his services at the present. Said he'd be back this afternoon, though. . . . And speaking of doctors, I telephoned to Doc Doremus[8] and asked him to hop out here. I figured it was Sunday and I might not be able to catch him later; and we'll have Montague's body in a little while."

    "Your men have got the pool gates closed then?"

    "Sure. But it was a tough job. One of the gates had got water-logged. Anyway, they're all set now. Luckily the stream was pretty low and there wasn't much of a flow of water. The dam lock was corroded, too, but we hammered it open. It'll take about another hour for the pool to drain, according to Stamm. . . . By the way, he wanted to go down and supervise the operations, but I told him we could get along without him."

    "It was just as well," nodded Vance. "Have your men put a screen of some kind over the lock in the dam? The body might go through, don't y' know."

    "I thought of that too," Heath returned with a little self-satisfaction. "But it's all right. There was a coarse wire mesh already over the lock."

    "Any visitors at the house this morning?" Vance asked next.

    "Nobody, sir. They wouldn't have got in anyway. Burke and Hennessey and Snitkin are back on the job this morning—I had another bunch of fellows here last night guarding the place. Snitkin is at the east gate, and Burke's here in the vestibule. Hennessey's down at the pool seeing that nobody approaches from that direction." Heath looked at Vance with an uneasy, questioning eye. "What do you want to do first, sir? Maybe you want to interview Miss Stamm and this young Tatum. There's something wrong about both of 'em, if you ask me."

    "No," drawled Vance. "I don't think we'll chivy the members of the household just yet. I'd like to meander round the grounds first. But suppose you ask Mr. Stamm to join us, Sergeant."

    Heath hesitated a second; then went into the house. A few moments later he returned accompanied by Rudolf Stamm.

    Stamm was dressed in gray tweed plus fours and a gray silk sleeveless sport shirt open at the throat. He wore no coat and was bareheaded. His face was pale and drawn, and there were hollows under his eyes, but his gait was steady as he came down the steps toward us.

    He greeted us pleasantly and, I thought, a bit diffidently.

    "Good morning, gentlemen. Sorry I was so crotchety last night. Forgive me. I was under the weather—and unstrung. . . ."

    "That's quite all right," Vance assured him. "We understand perfectly—a dashed tryin' situation. . . . We're thinking of looking over the estate a bit, especially down by the pool, and we thought you'd be good enough to pilot us around."

    "Delighted." Stamm led the way down a path on the north side of the house. "It's a unique place I've got here. Nothing quite like it in New York—or in any other city, for that matter."

    We followed him past the head of the steps that led down to the pool, and on toward the rear of the house. We came presently to a slight embankment at the foot of which ran a narrow concrete road.

    "This is the East Road," Stamm explained. "My father built it many years ago. It runs down the hill through those trees and joins one of the old roadways just outside the boundary of the estate."

    "And where does the old roadway lead?" asked Vance.

    "Nowhere in particular. It passes along the Bird Refuge toward the south end of the Clove, and there it divides. One branch goes to the Shell Bed and the Indian Cave to the north, and joins the road which circles the headland and connects with the River Road. The other branch runs down by the Green Hill and turns into Payson Avenue north of the Military Ovens. But we rarely use the road—it's not in good condition."

    We walked down the embankment. To our right, and to the southeast of the house, stood a large garage, with a cement turning-space in front of it.

    "An inconvenient place for the garage," Stamm remarked. "But it was the best we could do. If we'd placed it in front of the house it would have spoiled the vista. However, I extended the cement road to the front of the house on the south side there."

    "And this East Road runs past the pool?" Vance was glancing down the wooded hill toward the little valley.

    "That's right," Stamm nodded, "though the road doesn't go within fifty yards of it."

    "Suppose we waddle down," suggested Vance. "And then we can return to the house by way of the pool steps—eh, what?"

    Stamm seemed pleased and not a little proud to show us the way. We walked down the sloping hill, across the short concrete bridge over the creek which fed the pool, and, circling a little to the left, got a clear view of the high stone cliff which formed the north boundary of the pool. A few feet ahead of us was a narrow cement walk—perhaps eighteen inches wide—which led off at right angles to the road in the direction of the pool.

    Stamm turned into the walk, and we followed him. On either side of us were dense trees and underbrush, and it was not until we had come to the low opening at the northeast corner of the pool, between the cliff and the filter, that we were able to take our bearings accurately. From this point we could look diagonally across the pool to the Stamm mansion which stood on the top of the hill opposite.

    The water-level of the pool was noticeably lower. In fact, half of the bottom—the shallow half nearest the cliff—was already exposed, and there remained only a channel of water, perhaps twenty feet wide, on the opposite side, nearest the house. And even this water was sinking perceptibly as it ran through the lock at the bottom of the dam.

    The gates above the filter, immediately on our left, were tightly closed, thus acting as an upper dam and creating a miniature pond to the east of the pool. Fortunately, at this time of year the flow of the stream was less abundant than usual, and there was no danger that the water would reach the top of the gates or overflow its banks for several hours. Only a negligible amount of water trickled through the crack between the gates.

    As yet the dead man had not come into view, and Heath, scanning the surface of the pool perplexedly, remarked that Montague must have met his death in the deep channel on the other side.

    Directly ahead of us, within a few feet of the cliff, the apex of a large conical piece of jagged rock was partly imbedded in the muddy soil, like a huge inverted stalagmite. Stamm pointed at it.

    "There's that damned rock I told you about," he said. "That's where you got your splash last night. I've been afraid for weeks it would fall into the pool. Luckily it didn't hit anybody, although I warned every one not to get too close to the cliff if they went swimming. . . . Now I suppose it will have to be dragged out. A mean job."

    His eyes roamed over the pool. Only a narrow channel of water now remained along the concrete wall on the far side. And there was still no indication of the dead man.

    "I guess Montague must have bumped his head just off the end of the spring-board," Stamm commented sourly. "Damn shame it had to happen. People are always getting drowned here. The pool is unlucky as the devil."

    "What devil?" asked Vance, without glancing up. "The Piasa?"[9]

    Stamm shot Vance a quick look and made a disdainful noise which was half a laugh.

    "I see that you, too, have been listening to those crazy yarns. Good Lord! the old wives will soon have me believing there's a man-eating dragon in this pool. . . . By the way, where did you get that term Piasa? The word the Indians round here use for the dragon is Amangemokdom. I haven't heard the word Piasa for many years, and then it was used by an old Indian chief from out West who was visiting here. Quite an impressive old fellow. And I shall always remember his hair-raising description of the Piasa."

    "Piasa and Amangemokdom mean practically the same thing—a dragon-monster," Vance returned in a low voice, his eyes still focused on the gradually receding water on the floor of the pool. "Different dialects, don't y' know. Amangemokdom was used by the Lenapes,[10] but the Algonkian Indians along the Mississippi called their devil-dragon the Piasa."

    The water remaining in the channel seemed to be running out more swiftly now, and Stamm started to walk across the small flat area of sod at the edge of the pool, in order, I presume, to get a better view; but Vance caught him quickly by the arm.

    "Sorry and all that," he said a bit peremptorily; "but we may have to go over this patch of ground for footprints. . . ."

    Stamm looked at him with questioning surprise, and Vance added:

    "Silly idea, I know. But it occurred to us that Montague might have swum across the pool to this opening and walked away."

    Stamm's jaw dropped.

    "Why, in God's name, should he do that?"

    "I'm sure I don't know," Vance replied lightly. "He probably didn't. But if there's no body in the pool it will be most embarrassin'. And we'll have to account for his disappearance, don't y' know."

    "Tommy-rot!" Stamm seemed thoroughly disgusted. "The body'll be here all right. You can't make a voodoo mystery out of a simple drowning."

    "By the by," inquired Vance, "what sort of soil is on the bottom of this pool?"

    "Hard and sandy," Stamm said, still rankled by Vance's former remark. "At one time I thought of putting in a cement bottom, but decided it wouldn't be any better than what was already there. And it keeps pretty clean, too. That accumulation of muddy silt you see is only an inch or so deep. When the water gets out of the pool you can walk over the whole bottom in a pair of rubbers without soiling your shoes."

    The water in the pool was now but a stream scarcely three feet wide, and I knew it would be only a matter of minutes before the entire surface of the basin would be visible. The five of us—Vance, Markham, Heath, Stamm and myself—stood in a line at the end of the cement walk, looking out intently over the draining pool. The water at the upper end of the channel had disappeared, and, as the rest of the constantly narrowing stream flowed through the lock, the bottom of the channel gradually came into view.

    We watched this receding line as it moved downward toward the dam, foot by foot. It reached the cabañas, and passed them. It approached the springboard, and I felt a curious tension in my nerves. . . . It reached the spring-board—then passed it, and moved down along the cement wall to the lock. A strange tingling sensation came over me, and, though I seemed to be held fascinated, I managed to drag my eyes away from the rapidly diminishing water and look at the four men beside me.

    Stamm's mouth was open, and his eyes were fixed as if in hypnosis. Markham was frowning in deep perplexity. Heath's face was set and rigid. Vance was smoking placidly, his eyebrows slightly raised in a cynical arc; and there was the suggestion of a grim smile on his ascetic mouth.

    I turned my gaze back to the lock in the dam. . . . All the water had now gone through it. . . .

    At that moment there rang out across the hot sultry air, a hysterical shriek followed by high-pitched gloating laughter. We all looked up, startled; and there, on the third-floor balcony of the old mansion, stood the wizened figure of Matilda Stamm, her arms outstretched and waving toward the pool.

    For a moment the significance of this distracting and blood-chilling interlude escaped me. But then, suddenly, I realized the meaning of it. From where we stood we could see every square foot of the empty basin of the pool.

    And there was no sign of a body!