But the space-rats, Halleck and Gately, had no intention of waiting that long. They planned to expose the crystals for the shortest possible time and then sell them to unsuspecting citizens of Earth. Another thought struck Simms. Sterns! What had killed him? * * * * * He had the answer an instant later. Up on the wall a warning bell sounded and a red light flashed off and on. From a microtone speaker sounded that same deep-toned drone. Again it began to mount swiftly up the octaves, rising steadily to a high-pitched shriek preparing the way for the supersonic vibrations of the _Hudrites_. The lieutenant clapped his hands to his ears, fell to the floor in writhing agony. Stabbing lancets of pain darted through his brain. He felt his eyes protruding; his head seemed ready to explode. With a mighty effort he managed to jerk on his dehydration mask, slide the protective ear-caps into place. Even then the sensation was only partly relieved, and he stood, heart pounding, waiting for the mad vibration to stop. When at length it came to an end, a glance at the _Deleon_ Salts showed him they had colored from a light yellow to a deep orange. Tiny facets of irridescent flame now played over their surfaces. Whatever method of utilizing the supersonic field the Kamalis used, it was a deadly one. As the body of Sterns proved, the action of those piezo-electric crystals was fatal to the unprotected human organism. Simms moved to the control panel. He had the secret of the _Deleon_ Salts now. But what good would it do him. In a short time his escape would be detected and.... But even as his gaze sped over the dials, a thought struck him. One of those dials must control the intervals of time between each supersonic bombardment. Another must control the frequency of the vibrations. Boldly Simms seized a rheostat and shoved it over to its farthest marking. He found the time dial and pushed that upward too, guessing at the length of increase. Then he was descending swiftly the spiral staircase to the ground level. He skirted the main street of the village and groped his way through inky blackness to the swamp shore. In the gloom he made out his _jagua_. But he didn't stop here. He ran blindly a hundred yards along the matting shore until a squat beetle-like shape materialized out of the darkness. The space-rats' hydrocar. In a half minute he had the mooring line unfastened. And then splitting the darkness about him came a shaft of white light. Simultaneously Halleck's voice yelled: "Get him before he gets into the car!" There was a dull report like a melon striking, and something soft and fuzzy whizzed past Simms' head to hit the water with a hollow plop. A mold gun! In the relentless light of Halleck's search lamp, the lieutenant saw the living fungus erupt into a hundred wriggling spores that germinated in a matter of seconds.