"Well, at least," Gates reflected, "I can't be seen--that's one strategic advantage." But it would take more than his invisibility to win the battle. He must have weapons--weapons of unrivalled power. And where could such be found? * * * * * At this thought he remembered a certain invention he had toyed with months before. This was a knife which he called the Electric Blade: a folding strip of metal, small and compact, and short enough to be carried in a man's hip pocket, yet capable of being extended to the length of one's forearm, when it would cut with the sharpness of a sword. To it was attached a minute but powerful storage battery which Gates had perfected: a battery that made it possible for the blade to slash back and forth with such swiftness that the eye could hardly follow its motions. The inventor had believed that the weapon might prove valuable for close combat work in warfare; but had lost interest in it temporarily while working on that still more important device, the Infra-Red Eye. It was, however, with the greatest of enthusiasm that he thought now of the Electric Blade. Might this not be just what he needed in the conflict with Dunbar? Knowing something of the prowess of the Saturnians, he was far from sure; nevertheless, he swore a bitter oath, "I'll have a try at it, even if they hack me to mincemeat!"--which, he realized, they were only too likely to do. The Electric Blade, he recalled, had been left in his locker at the Merlin Research Institute. Accordingly, it was to this spot that he must hasten immediately upon returning to the city. It was night by the time he had reached the building; and the front door was locked. But seeing a light inside, he rapped. As no answer came, he rapped again, this time more loudly; and then rapped once more, still more loudly. It was only after the fourth or fifth summons that he heard shuffling footsteps warily approaching. "What the devil!" he muttered to himself. "Do they think I want to steal the building?" "Who's there?" a voice from within demanded, huskily. "It's I! Ronald Gates! An employee of the Institute!" There was a momentary hesitation. He heard two men conferring in whispers; then the door opened a few inches, and he stared into the muzzle of a revolver, behind which glowered the grim, determined face of a uniformed man. "Don't be scared, Officer," he began, slightly amused. "I can establish my identity--" Instantly there rang out a yell from the uniformed man. Savagely the door banged to a close. "By God! It's one of them devils from Saturn!" Almost simultaneously, he heard another voice taking up the cry. "Run, Miss, run! Quick! Ain't no time to waste! One of them fiends is after you again!" From within, he heard a woman's scream. "Out this way! This way!" And all other sounds were lost amid the scurrying of feet. But had those tones not had a familiar ring? Could it be--or was his heated imagination only playing tricks?