We went into Brisbane Coe's room, which was at the front of the house on the west side. It was a long narrow room, somewhat the shape of Archer's, with a large bay window on the street. It was simply furnished, but a series of large oak cabinets about the walls gave it an overcrowded, massive appearance. On the north wall beside the window was a series of simple built-in book-shelves extending to the ceiling. There were, I estimated, between three and four hundred volumes on them, all neatly and meticulously arranged.

    Vance went to the window and threw up the shades. Then he drew a chair to the book-shelves, mounted it, and began running his eye systematically over the volumes. I stood behind him and glanced over the titles. Markham and Heath sat down on a long davenport before the fireplace and watched Vance with an air of boredom.

    For so small a number of criminological volumes Brisbane Coe's collection was unusually complete. He had Hargrave L. Adam's complete "Police Encyclopædia" of Scotland Yard; the Complete Newgate Calendar; the Notable British Trials Series; Doctor Hans Gross's great handbook for examining magistrates; Dumas' "Celebrated Crimes"; Gayot de Pitaval's "Causes Célèbres et Intéressantes, avec les Jugemens qui les ont décidées"; Maurice Méjan's "Recueil des Causes Célèbres"; and many works in German including Kurt Langenscheidt's "Encyklopädie der Kriminalistik," a set of Der Wiener Pitaval, Friedlaender's "Kriminal-Prozesse," a set of Doctor Ludwig Altmann's "Aus dem Archiv des Grauen Hauses," and Leonhard's library of "Aussenseiter der Gesellschaft." In addition, there were various miscellaneous volumes dealing with criminals and their methods, but very little on the psychology of crime or its medico-legal aspects.

    In surveying the titles one got the impression that, had Brisbane gone in for crime, he would have been highly practical rather than subtle. The three lower shelves were devoted almost entirely to the classics of detective fiction, from Gaboriau and Poe to A. Conan Doyle and Austin Freeman.

    Vance glanced over the books rapidly but carefully. There were but few that were not in his own library, and he was familiar not only with their titles but with their appearance. He gave little attention, however, to the fiction. Just what he was looking for none of us knew; but we did know that he had some definite object in mind, and we suspected, from what he had said to us, that the object of his search related to the bolted door of Archer's bedroom.

    After scanning the backs of the books for perhaps fifteen minutes, he sat down and slowly lighted one of his Régies.

    "It should be here, y' know," he murmured, as if to himself, "—unless it's been taken away. . . ."

    He got up leisurely, and again standing on the chair, began to check the volume numbers of the various sets of books. When he came to the red-and-gold set of the "Aussenseiter der Gesellschaft" he gave a nod and stepped down to the floor.

    "A volume missing," he announced. He scanned the upper book-shelves carefully. "I wonder. . . ." Then he dropped on his knees and began going more thoroughly over the section of fiction.

    When he had come to the lowest shelf he reached forward and took out a thin red-and-gold volume. He glanced at it and leant forward again to inspect the books on either side of the space from which he had extracted the missing volume of the "Aussenseiter der Gesellschaft" series.

    "Oh, I say!" he exclaimed. "That's deuced interestin'." He pulled out a small red book. "'The Clue of the New Pin,' by Edgar Wallace," he read aloud.[20] "Only, we have two pins and a darning-needle—eh, what? . . . Still, Markham, it's significant that the missing volume of the 'Aussenseiter der Gesellschaft' should be found cheek by jowl with a book dealing with a pin."

    Markham took his cigar from his mouth, stood up, and faced Vance with a serious face.

    "I see what you mean," he said. "You think that Brisbane, by the help of these books on criminology, worked out some way of bolting Archer's door from the outside, by the use of those pins and string."

    Vance gave an affirmative nod.

    "Either Brisbane or some one else. It was quite a technical operation." He picked up the "Aussenseiter der Gesellschaft" volume and glanced at the title page. "'Der Merkwürdige Fall Konrad,'" he read. "By Kurt Bernstein. . . . That doesn't tell us much. I wonder who Konrad might have been and what subtleties he engaged in. . . . I think I'll do a bit of pryin' into Konrad's criminal past. And I'll glance through Wallace—if you could bear to wait for me a short while."

    Markham made a gesture of acquiescence.

    "The Sergeant and I will wait downstairs—I've some telephoning to do."

    The three of us left Vance alone in Brisbane's room, and as I closed the door I saw Vance stretch himself out on the davenport with the two books.

    An hour later he came to the head of the stairs and called down to us. We joined him in Archer's bedroom. He had both books with him, and I noticed that there were pages marked in each.

    "I think I've found a solution to one phase of our problem," he announced seriously, when we were seated. "But it may take a bit of working out." He opened the novel. "Wallace has a clever idea here—I found the passage without too long a search. The tale, as I gather at a hasty reading, relates of a dead man found locked in a vault with the key to the door on the table before him. The vault door was locked from the outside, of course. . . . Here's the explanat'ry passage: 'No other word he spoke, but took something from his pocket: it was a reel of stout cotton. Then from his waistcoat he produced a new pin, and with great care and solemnity tied the thread to the end of the pin, Tab watching him intently. And all the time he was working, Rex Lander was humming a little tune, as though he were engaged in the most innocent occupation. Presently he stuck the point of the pin in the centre of the table, and pulled at it by the thread he had fastened. Apparently he was satisfied. He unwound a further length of cotton, and when he had sufficient he threaded the key upon it, carrying it well outside the door. The end he brought back into the vault, and then pushed it out again from the inside through one of the air-holes. Then he closed the door carefully. He had left plenty of slack for his purpose and Tab heard the click of the lock as it was fastened, and his heart sank. He watched the door fascinated, and saw that Lander was pulling the slack of the cotton through the air-hole. Presently the key came in sight under the door. Higher and higher came the sagging line of cotton and the key rose until it was at the table's level, slid down the taut cotton, and came to rest on the table. Tighter drew the strain of the thread, and presently the pin came out, passed through the hole in the key, leaving it in the exact centre of the table. Tab watched the bright pin as it was pulled across the floor and through the ventilator.'[21] . . . That's the way Wallace worked his locked door."

    "But," objected Markham. "There was an open ventilator in the door, and space beneath the door. Those conditions are not true here."

    "Yes—of course," Vance returned. "But don't overlook the fact that there was a string and a bent pin. At least they are common integers in the two problems. . . . Now, let's see if we can combine those integers with certain common integers of the Konrad case." He opened the other book. "Konrad," Vance explained, "was a truck-driver in Berlin nearly fifty years ago. His wife and five children were found dead in their cellar room; and the door—a ponderous affair without even a keyhole or space around the moulding—was securely bolted on the inside. The case was at once pronounced one of murder and suicide on the part of the mother; and Konrad would have been free to marry his inamorata (whom he had in the offing) had it not been for an examining magistrate of the criminal court, named Hollmann. Hollmann, for no tangible reason, did not believe in the suicide theory, and set to work to figure out how Konrad could have bolted the door from without. . . . Here's the revelat'ry passage—if you'll forgive my rather sketchy sight translation of the German: 'Hollmann, urged on by his conviction that Frau Konrad had not murdered her children and committed suicide, determined, as a last resort, to give the entire door, both inside and outside, a microscopic examination. But there was not the slightest aperture anywhere, and the door fitted so tightly around the frame that a piece of paper could not have been passed through any crevice. Hollmann examined the door minutely with a powerful lens. It required hours of labor, but in the end he was rewarded. Just above the bolt he found on the inside, close to the edge of the door, a very small hole which was barely discernible. Opening the door he inspected the outside surface directly opposite to the hole on the inside. But there was no corresponding hole visible. Hollmann did find on the outside of the door, however, a small spot on which the paint seemed fresher than that on the rest of the door. The spot was solid, but this did not deter Hollmann's investigation. He borrowed a hatpin from one of the tenants in the building, and heating it, ran it through the hole on the inside. With but little pressure the heated hatpin penetrated the door, coming out on the outside exactly in the centre of the newly painted spot. Moreover, when Hollmann withdrew the hatpin a piece of tough horsehair adhered to the pin; and on the pin was also discernible a slight film of wax. . . . It was obvious then how Konrad had bolted the door from without. He had first bored a tiny hole through the door above the bolt, looped a piece of horsehair over the bolt's knob, and slipped the two ends through the hole. He had then pulled the bolt-knob upward until the horsehair loop was disengaged, withdrawing the horsehair through the hole. A piece of the horsehair had, however, caught in the hole and remained there. Konrad had then filled up the hole with wax and painted it on the outside, thereby eliminating practically every trace of his criminal device. He was later convicted of the murder of his family, sentenced to death, and hanged.' . . ."[22]

    Heath, as Vance finished reading, leapt to his feet.

    "That's a new one on me." He went swiftly to the door and bent over.

    Vance smiled.

    "There's no hole in the door above the bolt, Sergeant," he said. "No need, don't y' know. There's a keyhole."

    Heath squared off and looked at the door.

    "Still and all, the keyhole's only half-way over the bolt, and eight inches below it. No string fastened to the bolt and run through that keyhole would lock the room from the outside."

    "True, Sergeant," Vance nodded. "But that's where the modification of the trick comes in. The person who planned bolting this door carried the idea to a few more decimal points. Don't forget we have two pieces of string and two pins."

    "Well, I don't get it." Heath still stood scowling at the door. "The cases in those two books are easy enough to understand, but neither of 'em will work here."

    "Maybe the two together will work," suggested Vance. "Look at the wall just to the right of the jamb and opposite to the bolt. Do you see anything?"

    Heath looked closely, using his pocket magnifying glass and his flashlight.

    "I don't see much," he grumbled. "Right in the crack of the jamb and wall there's what might be a pinhole."

    "That's it, Sergeant!" Vance rose and went to the door; and Markham and I followed him. "I think I'll try the experiment I have in mind."

    We all watched him with fascinated interest. First he reached in his pocket and drew forth the two pieces of string and bent pins and the darning-needle he had found in the pocket of Brisbane Coe's overcoat. By means of his pocket knife he straightened one of the pins and inserted it in the hole Heath had found in the wall at the edge of the jamb, giving it several taps with the handle of his knife to drive it in rather securely. He then threaded the other end of the string in the darning-needle and passed it through the keyhole into the hall, removing the needle and letting the string fall to the hall floor. After this operation, he bent the other pin securely round the upright knob of the bolt, passed the string over the pin he had driven into the wall, and, threading this second string into the darning-needle, passed it also through the keyhole to the hall. He then opened the door about eighteen inches, drawing the two strings partly back through the keyhole in a loop to permit the door to swing inward without disturbing his mechanism.

    "Let us see if the device works," he said, with an undercurrent of suppressed excitement. "You stay in the room while I go outside and manipulate the strings."

    He bent down and passed under the two strings into the hall. Then he closed the door gently, while we remained inside, our eyes riveted to the two strings and the two pins.

    Presently we saw the string which was attached to the bolt-knob go taut, as Vance drew it slowly through the keyhole. Passing over the pin in the wall, which acted as a pulley, the string described a sharp angle, with the pin in the wall as the apex. Slowly Vance drew the string from outside, and the bolt, getting a straight pull around the pin, began to move into its socket on the jamb. The door was bolted!

    The next thing we saw was the tightening of the other string—the one attached to the head of the pin in the wall. There came several jerks on the string—the pin in the wall resisted several times and bent toward the source of the pull. Finally, it was disengaged from the wall; and it was then drawn upward from its depending position, disappearing through the keyhole.

    The other string, still hooked about the bolt-knob, was then drawn taut through the keyhole, describing a straight line from the bolt-knob to the keyhole which was almost directly below it. Another slight pull by Vance on the string, and the knob fell downward into its groove. Another pull, and the bent pin was disengaged from the knob and pulled through the keyhole into the hall.

    Markham, Heath, and I had been bolted in the room from the hall as neatly as if we ourselves had shot the bolt and locked it. And there was no evidence of any kind—save the indiscernible pin-point hole in the crack of the wall—to show that it had not actually been bolted from the inside!

    Vance's demonstration had been fascinating and, at the same time, sinister; for it had brought up vague and unplumbed possibilities and revealed to us that we were battling against a shrewd and resourceful antagonist.

    The Sergeant, after a moment's stupefaction, threw back the bolt and opened the door.

    "It worked?" asked Vance, coming into the room.

    "It worked," mumbled Heath laconically, lighting the cigar he had been chewing on viciously for the past half-hour.