Now she had called him in a voice that fairly trembled with excitement--and, he thought, dread! And she had been interrupted before she had time to give him any message. For a few seconds Larry stared at the telephone. Then he rose abruptly to his feet, crammed his hat on his head, and started for the door. "The way to find adventure is to go after it," he murmured. "And this is the invitation!" It was not many minutes later that he sprang out of a taxi at the front of the building in which Dr. Travis Whiting made his home and maintained a private experimental laboratory. It was a two-story stucco house, rather out of date, set well back from the sidewalk, with a scrap of lawn and a few straggling shrubs before it. The door was closed, the windows curtained blankly. The place seemed deserted and forbidding. Larry ran up the uneven brick walk to the door and rang the bell. Impatiently, he waited a few moments. No sound came from within. He felt something ominous, fateful, about the silent mystery that seemed to shroud the old house. For the first time, it occurred to him that Agnes might be in physical danger, as a result of some incautious experiment on the part of Dr. Whiting. * * * * * Instinctively, his hand sought the door knob. To his surprise, the door was unlocked. It swung open before him. For a moment he stared, hesitating, into the dark hall revealed beyond. Then, driven by the thought that Agnes might be in danger, he advanced impulsively. The several doors opening into the hall were closed. The one at the back, he knew, gave admittance to the laboratory. Impelled by some vague premonition, he hastened toward it down the long hall and threw it open. As he stepped inside the room, his foot slipped on a spot of something red. Recovering his balance with difficulty, he peered about. Bending down, Larry briefly examined the red spot on which he had slipped. It was a pool of fresh blood which had not yet darkened. Lying beside it, crimson-splashed, was a revolver. As he picked up the weapon, he cried out in astonishment. Something had happened to the gun. The trigger guard was torn from it, and the cylinder crushed as if in some resistless grasp; the stock was twisted, and the barrel bent almost into a circle. The revolver had been crumpled by some terrific force--as a soft clay model of it might have been broken by the pressure of a man's hand. "Crimson shades of Caesar!" he muttered, and dropped the crushed weapon to the floor again. His eyes swept the silent laboratory. It was a huge room, taking up all the rear part of the house, from the first floor to the roof. Gray daylight streamed through a sky-light, twenty feet overhead. The ends of the vast room were cluttered with electrical and chemical apparatus; but Larry's eye was caught at once by a strange and complex device, which loomed across from him, in the center of the floor. * * * * *