Smythe obtained a gun for her, and as she did not wish to wait for the slow elevator, she ran up the steps. Smythe could not tell her definitely what had occurred in the upper laboratory that had caused the museum to be closed for the day. Her heart beating swiftly, Betty Young hurried up the second flight of stairs to the third floor. A workman, whom the girl recognized as a manual laborer in the paleontological rooms, came running down, passing her in full flight, a look of abject terror on his face. "What is it?" she cried. He was so frightened he could not talk logically. "There was a black fog--I saw a red snake with legs--" She waited for no more. A pang of fear for the safety of Marable shot through her heart, and she forced herself on to the top floor. Up there was a haze, faintly black, which filled the corridors. As Betty Young drew closer to the door of the paleontological laboratories, the mist grew more opaque. It was as though a sooty fog permeated the air, and the girl could see it was pouring from the door of the laboratory in heavy coils. And her nostrils caught the strange odor of fetid musk. She was greatly frightened; but she gripped the gun and pushed on. * * * * * Then to her ears came the sound of a scream, the terrible scream of a mortally wounded man. Instinctively she knew it was not Marable, but she feared for the young professor, and with an answering cry she rushed into the smoky atmosphere of the outer laboratories. "Walter!" she called. But evidently he did not hear her, for no reply came. Or was it that something had happened to him? She paused on the threshold of the big room where were the amber blocks. About the vast floor space stood the numerous masses of stone and amber, some covered with immense canvas shrouds which made them look like ghost hillocks in the dimness. Betty Young stood, gasping in fright, clutching the pistol in her hand, trying to catch the sounds of men in that chamber of horror. She heard, then, a faint whimpering, and then noises which she identified in her mind as something being dragged along the marble flooring. A muffled scream, weak, reached her ears, and as she took a step forward, silence came. She listened longer, but now the sunlight coming through the window to make murky patches in the opaque black fog was her chief sensation. "Walter!" she called. "Go back, Betty, go back!" The mist seemed to muffle voices as well as obscure the vision. She advanced farther into the laboratory, trying to locate Marable. Bravely the girl pushed toward the biggest amber block. It was here that she felt instinctively that she would find the source of danger. "Leffler!" she heard Marable say, almost at her elbow, and the young man groaned. The girl came upon him, bending over something on the floor. * * * * *