the two skulkers soon disappeared, having drawn too close to the nearer wall for nick carter to see them. he put his ear close to the opening, however, and listened.

he was enabled to hear the ladder placed against the fire escape, faint though the sound was, and to check off the men’s movements as they climbed upward. when they approached the second floor, he quietly slipped out of his chair and retreated into the shadows in the middle of the room. he did not care to be seen at the window, even though his identity was so well cloaked.

apparently no word was exchanged on the part of the two climbers. they were running a considerable risk, and they doubtless knew it. there was quite enough light for them to be seen if any one should look out of one of the many windows which opened on the court. fortunately for them, however, they did not have far to go, and were not obliged to pass a single bedroom.

they made their way upward with a great deal of care, but nick could plainly hear the faint scrape of their shoes on the metal steps.

it was obvious that they had already settled all the details.

“they have everything cut and dried,” the detective told himself, his keen eyes glinting in the shadows, “and men of their type do not go to such deliberate pains for nothing.”

after that the sounds told the detective that the first man, probably stone himself, had reached the landing just to the right of his window, and almost immediately afterward he caught the faint noise made as the sash was raised.

there was a little more rustling and scraping, then silence. the detective concluded that it was safe enough to return to his point of vantage outside. just as he did so, he saw the lower sash of stone’s window being pulled down.

“i hope they leave that wedge in place,” he murmured.

the light flashed up, and the shade was drawn down—by doctor follansbee, as the shadow showed.

there was no way of telling, however, whether the wedge had been removed or not. follansbee had doubtless been the last to pass through, and probably did not know of its existence; and then it might have been dislodged by the passage of one or the other of them.

it was time for the watcher to become the man of action, and the transformation entailed considerable risk, as the detective knew. he did not mean to remain in idleness where he was; but, on the contrary, had determined to repeat his maneuver of some time before. in other words, he meant to crawl out on the fire escape once more and take a position outside of the miner’s window, in the hope that he could hear enough of the conversation between the two to enable him to get a clew to their intentions, if not with regard to winthrop crawford.

the sounds they had made with all their care had brought his danger home to him, and he realized that the necessity for climbing over the iron railing made it likely that he would cause even more noise. the attempt must be made, though, come what might, and nick had already made preparations for it. he had anticipated the necessity, and had previously transferred a little instrument from one of his suit cases to his pocket.

it was a sort of disc made of hard rubber for the most part, and about an inch in thickness. its use was obscure at first glance, but would have been sufficiently plain upon examination. it was a sort of ear trumpet designed for the deaf, but without the old-fashioned horn attachment.

he buttoned his coat once more about him, then proceeded to raise his window the required distance; but at the risk of missing something important, he took his time about it, with the result that the slight sound could not have been heard even a few feet away. when there was room enough for him to crawl through, he did so, and, leaning over, grasped the end of the platform. he stepped noiselessly across the gap, threw one leg over the railing and gently lowered himself to the grating. along this he tiptoed, his thin-soled shoes making practically no sound as he advanced. in a few moments he was kneeling in front of stone’s window with the rubber disc held to his right ear, and his ear lowered to the crack at the bottom of the sash.

the wooden wedge was still in place, luckily for him, consequently the sash had remained slightly raised. as soon as the device was brought into use, it amplified the sounds it caught, and what had been an indistinct murmur of voices became an easily audible conversation.

“be very careful of this,” were the first definite words he heard. they were in doctor follansbee’s voice. “i will leave it in the case here for you,” the high, thin tones went on. “don’t press the plunger until you have inserted the needle underneath the skin. is that clear?”

“yes.”

the detective hardly recognized stone’s voice, so hoarse and agitated did it sound.

“the drug and sponge will be easy for you to handle,” follansbee explained. “wait until you get into the room and are six feet or so from the bed, then just sprinkle a few drops on the sponge from this vial.”

“won’t he smell the stuff and wake up?”

“certainly not, unless you make a noise. the drug has a penetrating odor, of course, for the time being, but his sleeping sense won’t convey a message of warning soon enough to spoil your plans. if the odor reaches his nostrils before you’re ready to act, and he’s really asleep, it will probably only cause a momentary dream of some sort; an attempt of the subconscious self to explain the situation.”

“all right, but—but won’t they be able to tell that he’s been drugged?”

nick heard a thin, piping laugh. “you must think me a fool,” follansbee’s voice returned. “the keenest scent would be incapable of detecting any odor in the room five minutes after that drug is used, and it leaves little or no after effects. crawford will wake up to-morrow morning without the slightest suspicion that anything has happened to him, and he’ll feel perfectly normal.”

“and what about the—the other?”

“it will not begin to show itself until monday or tuesday,” was the confident answer. “and even then the symptoms will be inconclusive. there aren’t half a dozen physicians who would know what they meant in any of the early stages, and by the time any one could authoritatively diagnose the case, the patient would be beyond help. in fact, he’ll be beyond it for all ordinary purposes from the time the serum is introduced into his system, and before the twenty-seventh he’ll be dead.”