"Message from the enemy!" gasped Hart, George and I, echoing the words like parrots. "Yes. A demand that the United States surrender, and a threat to descend into the lower levels if the demand is not complied with in twenty-four hours!" "Who is this enemy?" asked Hart, "and where?" "Who they are is not known," replied the official gravely; "and as to the location, the War Department is puzzled. Direction finders throughout the country took readings on the position of their radio transmitter and these readings differed widely in result. But the consensus of opinion is that the messages originate somewhere out in space, probably between fifty and one hundred thousand miles from our earth." "Great guns!" Hart glanced at George and me, where we stood with stupidly hanging jaws. "And what does the government want of me now?" "You are considered to be the one man who might be able to cope with the problem, and are ordered to report to the Secretary of War, in person, immediately." * * * * * Hart was electrified into instant activity. "Here," he said in a voice of authority that commanded the official's attention and respect, "see that this package of bonds is delivered at once to the addressee and that the addressor is advised of its safe arrival. We're off at once." Suiting action to the words, he thrust my packet into the hands of the astonished supervisor. Then, turning sharply on his heel, he flung back, "Advise the Secretary of War that I shall report to him in person in less than one hour." As we stepped through the entrance of the _Pioneer_, he shot a final look at the official and laughed heartily at his sudden accession of energy. We had not the slightest doubt that Hart's orders would be immediately and efficiently carried out. * * * * * In precisely forty-five minutes, we stood before the desk of Lawrence Simler, then Secretary of War, in Washington. "You are Mr. Hartley Jones?" inquired the stern-visaged little man. "I am, Mr. Secretary, and these are my friends and co-workers, George Boehm and John Makely." The Secretary acknowledged the introduction gravely, then plunged into the heart of the matter at hand with the quick energy for which he was famed. "It may or may not be a serious situation," he said, "but certainly it has thus far been quite alarming. In any event, we have taken the matter out of the hands of the Air Traffic Bureau. We are prepared to defy the ultimatum of the enemy, whoever he may be. But we want your help, Mr. Jones. Every ship of the Air Navy will be in the upper levels within the prescribed twenty-four hours, and we will endeavor to stave off their attacks until such time as you can fit the _Pioneer_ for a journey to their headquarters." "How can your antiquated war vessels, capable of hurling a high explosive shell no more than fifty miles, fight off an enemy that is thousands of miles distant?" asked Hart.