It was not long before that victim responded to the call. On the departure of the manager from the room Grace Lee rose, and with a conscious look toward the two clerks, slipped across the floor to the open door of the safe room. Entering, she swung to the door, which closed with a snap; then, with just a moment of hesitation, in which she seemed to be trying to regain her breath, she passed quickly across to the safe and took up her stand before it. So directly and so quickly had she done this that she had not seen the slim, immovable figure drawn up against the wall at her right behind the projection of a large bookcase. Nor did any influence for good or evil cause her to turn after she had reached the safe. All her thoughts, all her hopes, all the dreams which she had cherished seemed to be concentrated in the blank, eyeless object which confronted her, impenetrable to all appearance--a block of steel without visible opening--an enigma among safes--the problem of all problems to every cracksman in town but one--which was about to be solved if one could judge from the thrill which now shook her, and in shaking her communicated the same excitement to the silent, breathless, determined man in her rear, watching her as the tiger watches the quarry, and with the same tiger spring latent in his eye. In a moment her secret would be out, and then---- CHAPTER XIII "_I am from headquarters_" For just a minute Grace Lee paused before the blank door of the safe, then she passed around to an unused speaking tube in the neighboring wall. Halting before it, in low but distinct tones she began to sing the famous aria from "The Magic Flute." All agog, with eyes starting and ears alert, the man behind listened and watched. Nothing happened. Then came a change. Gradually her voice rose, sweet and piercing, till it reached that famous F in alt so rarely attempted, so exciting to the ear when fairly taken and fairly held. Grace Lee could take it, and as it hung, sweet and deliciously thrilling in the air, Beau Johnson saw, to his amazement, though he was in a way prepared for it, the heavy safe door slip softly ajar. She had done it with her voice. How, he could only vaguely guess. He was better educated than most of his class, or he could not have understood it at all. As it was, he laid it to the vibration caused by a certain definite note acting on some delicate mechanism set in accord with that note, which mechanism starting another and a stronger one gradually led up to that which drew the bolts and set the door ajar. Whether his theory were true or not mattered little at the moment. The event for which he waited had been accomplished and accomplished before his eyes. To profit by it was his next thought, and to this end he held himself ready for the spring which had laid latent in his eyes since he first saw her advance toward the safe.