"We've got to be absolutely secret," Livingston said. He lowered his voice and flung a glance at the window oval where the moonlight was gleaming with a silver sheen. "There's big money involved in this. I'm going to trust you, John, but no one else." "What is it?" I murmured. A little half-smile of excited triumph was playing about his thin lips. "Let me ask you," he said, "have you ever heard of Xalite?" "Well--just vaguely." "The new element which was discovered a few years ago. I needn't explain its technical uses--" "A germ-killer," I said. "I remember hearing a technological newscast--you bombard diseased tissues--" "Exactly. To kill certain virulent germs without injuring the living human tissue. And they're thinking now they could use it in the new atomic engines--perhaps the one thing which would make them really commercially practical--" "Except that Xalite costs about ten thousand gold-dollars a grain," I observed. "Quite so. As a matter of fact, what little was discovered here on earth is now in use. No more can be found--and it's an unstable element. Within another year we will have no Xalite." He paused, and then abruptly he added, still more softly, "I've discovered an unlimited quantity, John. Xalite in quantity beyond anyone's wildest dreams--" "Where?" I gasped. "Not here on earth. Don't you see how it fits with our plans for the _Planeteer_?" I sat silent, tense as he told me. There was, this year, coming in from the realms of Interplanetary space, a little asteroid. Astronomers for their charts had named it Zura--a dark, cold little world of perhaps five hundred miles diameter. "It seems this is its second visit," he said. "Some sixteen years ago it first made its appearance--came into our Solar System, rounded the Sun and went out again. The elements of its orbit, sixteen years ago, were computed. A narrow ellipse, taking it in between Mercury and Vulcan, and out beyond Pluto." * * * * * In his laboratory here, Dr. Livingston had erected a small, but ultra-modern, electroscope. He took me to it now. The dark little Zura, he told me, already had cut the orbit of Mars and was fairly close to us. It was in the northern sky now, near the zenith. The night was clear, glittering with a myriad stars like gems profusely strewn on the deep purple velvet of the Heavens. I gazed at little Zura as he swung the high-powered little instrument almost to its full intensity of magnification. What I saw was a round, blurred, dark-gray disc, dimly mottled with heavy cloudbanks. "What has this to do with us, and Xalite?" I murmured. "I'll show you, John. If we can get a break in those clouds--it sometimes occurs--"