Thurston shook his head. "They are back," said the Secretary. "Reported over London--Paris--the West Coast. Even China has seen them. Shanghai cabled an hour ago." "Them? How many are there?" "Nobody knows. There were five seen at one time. There are more--unless the same ones go around the world in a matter of minutes." * * * * * Thurston remembered that whirlwind of vapor and a vanishing speck in the Arizona sky. "They could," he asserted. "They're faster than anything on earth. Though what drives them ... that gas--steam--whatever it is...." "Hydrogen," stated General Lozier. "I saw the New York show when poor Davis got his. He flew into the exhaust; it went off like a million bombs. Characteristic hydrogen flame trailed the damn thing up out of sight--a tail of blue fire." "And cold," stated Thurston. "Hot as a Bunsen burner," the General contradicted. "Davis' plane almost melted." "Before it ignited," said the other. He told of the cold in their plane. "Ha!" The General spoke explosively. "That's expansion. That's a tip on their motive power. Expansion of gas. That accounts for the cold and the vapor. Suddenly expanded it would be intensely cold. The moisture of the air would condense, freeze. But how could they carry it? Or"--he frowned for a moment, brows drawn over deep-set gray eyes--"or generate it? But that's crazy--that's impossible!" "So is the whole matter," the Secretary reminded him. "With the information Mr. Thurston and Mr. Riley have given us, the whole affair is beyond any gage our past experience might supply. We start from the impossible, and we go--where? What is to be done?" "With your permission, sir, a number of things shall be done. It would be interesting to see what a squadron of planes might accomplish, diving on them from above. Or anti-aircraft fire." * * * * * "No," said the Secretary of War, "not yet. They have looked us over, but they have not attacked. For the present we do not know what they are. All of us have our suspicions--thoughts of interplanetary travel--thoughts too wild for serious utterance--but we know nothing. "Say nothing to the papers of what you have told me," he directed Thurston. "Lord knows their surmises are wild enough now. And for you, General, in the event of any hostile move, you will resist." "Your order was anticipated, sir." The General permitted himself a slight smile. "The air force is ready." "Of course," the Secretary of War nodded. "Meet me here to-night--nine o'clock." He included Thurston and Riley in the command. "We need to think ... to think ... and perhaps their mission is friendly." "Friendly!" The two flyers exchanged glances as they went to the door. And each knew what the other was seeing--a viscous ocherous mass that formed into a head where eyes devilish in their hate stared coldly into theirs....