The general’s face became haggard, and there was a trace of terror in his own eyes. “There is. Something even worse than the people must suspect.” Rob shuddered. All of a sudden the minus-200-degree temperature outside his space suit seemed to have penetrated inside. He checked the heater and found that it was all right. No, this was a mental chill. Next came the inevitable question, “What is this—thing?” “You and your crew will be sworn to strictest secrecy before you blast off from Luna,” General Forester said. “That pledge of secrecy for you begins at this instant. If the people back home got even an inkling of what the trouble is, there would be widespread panic.” “You have my word, sir,” Rob said. [Illustration: _That pledge of secrecy for you begins at this instant._] There followed an electric silence for several moments. It was as if the general himself were rallying courage. “There is a giant radioactive cloud approaching the solar system from outer space at a terrific speed. The cloud covers an area roughly as big as Jupiter. Scientists have been plotting its trajectory with electronic instruments for a long time, and there is no doubt but that it will collide with the system if nothing is done about it. Life, of course, would be wiped out completely.” Rob felt the horror of the statement clear to the marrow of his bones. It left him shaking and numb. The general noticed the effect on him. “That’s the way it left me when I first heard about it,” he admitted. “If it affects us two, who are reasonably adjusted to the terrors of space, how do you think it would affect ordinary persons?” After the shock had lessened somewhat, Rob was able to speak. “But you do have a weapon against this cloud?” he said hopefully. “We hope we have,” General Forester replied. “It’s called Operation Big Boy.” There was no more time for discussion. The jeep topped a rise, just below which lay the hub of buildings making up the Space Command. Rob suffered further agony of suspense as they parked and glided over the sands to the general’s office in the main building. Rob was glad to get out of his space suit, for he had been in a cold sweat ever since he had heard the first sobering words about the cosmic terror. Rob and the general locked themselves in the privacy of the latter’s quarters. “The appearance of the R-cloud, as we call it, has necessitated using our topmost military weapon,” General Forester resumed. “You and no one else except the World Security Commission has known that the Space Command has had for some time a stockpile of cosmic-ray bombs which could literally blow Earth apart. You and your crew will carry a set of these bombs and try to scatter the mass so that it won’t penetrate the solar system. But of course there’s no assurance that the bombs can do this.”