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 ............