The buzz of a motorcycle being raced at high speed jarred on the quiet of the yard outside the factory. The electrician cast an annoyed glance in the direction of the rider. The machine stopped in front of the power house and Dixie Mason slipped from the seat. She saw the electrician cast a hurried glance at her over his shoulder and she hesitated. Was she too late to stop him from carrying out his plan whatever it was? Could she stop him? An attempt to stop the spy might fail, but she could at least warn the people of their danger. She ran into the building. Past long lines of workers she dashed screaming in a shrill voice that echoed above the roar of machinery: "Out! Out! Everybody!" The workers, ever conscious of the hazards under which they labored and alert for the slightest token of danger, left their work tables and rushed for exits, taking up the cry as they passed other workers. Dixie seeing that her warning was being obeyed ran back to the power house. The yard was filled with hurrying, shrieking, excited women. The electrician at the sound of shouting and confusion had stepped to the door. As he saw Dixie rushing toward him, he knew the success of his plans was frustrated. [Illustration: A munitions plant destroyed by the Kaiser's agents] He turned quickly to the switch. At the same moment, Dixie, knowing intuitively that this was his plan of destruction, threw her slight body at him and clung to him with a catlike tenacity, striving to stay the hand that was reaching for the switch. With a curse his great hand closed around her throat. Still she struggled but he held her now at a distance and leaned forward. She heard the switch jammed shut with a crackling contact. A second later the darkness without was pierced by a wild burst of flames, and the earth heaved and rocked with the impact of an earthquake. But Dixie Mason heard it only vaguely. She had fainted and was lying against the switch, one hand still in unconsciousness clinging to it as though the hope yet lived that she could prevent the awful catastrophe that had fallen. Through the clouds of dust and smoke, through the crowds of injured workers, through debris piled high from which little tongues of flame were shooting, Harrison Grant reached the power house. When Dixie returned to consciousness it was to find him bending over her. For one glad moment she recognized him. She struggled to rise. "You!" she said, but Grant's voice, cold and unfriendly, dispelled the hopes that had risen within her. "Yes. Miss Mason, I'm afraid you will have a somewhat difficult time in explaining your presence here beside the switch that has blown up the factory." In spite of weakness Dixie straightened up. Her lips parted and she reached involuntarily toward the pocket that held her Secret Service Commission. But the impulse was checked, for the orders she had received months before flashed through her throbbing brain: "Work into the trust of the Germans. Tell no one.