Nick waited, lest the stair might creak again if he stirred. Bending nearer the baluster rail, nevertheless, he could see through the open door of the opposite room. It was the library of the handsomely furnished house. With the exception of one part of the room, all was invisible, shrouded in inky darkness. The exception was a circle of light shed upon an open desk--faintly revealing a figure crouching in front of it. It appeared to be that of a man engaged in robbing the desk, or quietly forcing the interior drawers in search of something. Nick waited and watched. "By Jove, here’s a curious coincidence," he said to himself. "Have I stolen in here just in time to catch a crook? Apparently, however, I’m in his class. He may, on the other hand, be some one who lives in the house and who has some motive for stealthily searching that desk. No, by gracious, that’s not probable. He certainly is a crook." The figure crouching at the desk had turned slightly and gazed toward the hall, as if under the impulse of sudden uneasiness, or that subtle sense which at times impresses one of the presence of another. Nick then saw that the lower part of the man’s face was covered with a black cloth--convincing him that he was a thief from outside, rather than a resident of the house. He turned, after listening for a moment, and resumed his knavish work. Nick Carter’s first impulse was to arrest the thief then and there--but he did not do so. Another and better move, in view of the greater possibilities it presented, quickly occurred to him. "By Jove, this may be the opportunity of a lifetime," he said to himself. "It’s odds that the rascal is not alone, that he has one confederate, at least, who may be watching outside, probably in the rear of the house. I can fool this scamp and gather in both of them, I think, or even round up a bigger gang with which they may be identified. That surely would discount taking in only this fellow. I’m blessed if I don’t try it." Nick had recalled his sinister make-up, also that he had several changes of disguise in his pocket. He deftly adjusted one over his already hangdog type of countenance, then glided quickly under the rise of stairs mentioned, crouching low against the baseboard in one corner. The top of the basement stairs creaked again when he left them, precisely as he had anticipated. The effect, moreover, was exactly what he was expecting. The figure at the library desk started up as if electrified by the faint sound. The circle of light from the flash lamp vanished instantly, leaving the room and hall in impenetrable gloom. "He heard it," thought Nick, holding his breath. "He’s waiting and listening. He fears that some one is here, but he is not sure." The waiting detective was right. He presently could hear the stealthy, catlike tread of the crook approaching the near door. It ceased after a moment, and Nick knew that the rascal then had reached the threshold and again was listening intently.