"You have the facts. We know who this self-styled Black Caesar is, who has declared war upon humanity. He is a Dane named Axelson, whose father, condemned to life imprisonment for resisting the new world-order, succeeded in obtaining possession of an interplanetary liner. "He filled it with the gang of desperate men who had been associated with him in his successful escape from the penitentiary. Together they sailed into Space. They disappeared. It was supposed that they had somehow met their death in the ether, beyond the range of human ken. "Thirty years passed, and then this son of Axelson, born, according to his own story, of a woman whom the father had persuaded to accompany him into Space, began to radio us. We thought at first it was some practical joker who was cutting in. [Illustration: _It was like struggling with some vampire creatures in a hideous dream._] "When our electricians demonstrated beyond doubt that the voice came from outer space, it was supposed that some one in our Moon Colony had acquired a transmitting machine. Then the ships we sent to the Moon Colony for gold failed to return. As you know, for seven weeks there has been no communication with the Moon. And at the last full moon the--blow--fell. "The world depends upon you, Lee. The invisible rays that destroyed every living thing from China to Australia--one-fifth of the human race--will fall upon the eastern seaboard of America when the moon is full again. That has been the gist of Axelson's repeated communications. "We shall look to you to return, either with the arch-enemy of the human race as your prisoner, or with the good news that mankind has been set free from the menace that overhangs it. "God bless you, my boy!" The President of the United States of the World gripped Nat's hand and stepped down the ladder that led from the landing-stage of the great interplanetary space-ship. * * * * * The immense landing-field reserved for the ships of the Interplanetary Line was situated a thousand feet above the heart of New York City, in Westchester County. It was a flat space set on the top of five great towers, strewn with electrified sand, whose glow had the property of dispersing the sea fogs. There, at rest upon what resembled nothing so much as iron claws, the long gray shape of the vacuum flyer bulked. Nat sneezed as he watched the operations of his men, for the common cold, or coryza, seemed likely to be the last of the germ diseases that would yield to medical science, and he had caught a bad one in the Capitol, while listening to the debate in the Senate upon the threat to humanity. And it was cold on the landing-stage, in contrast to the perpetual summer of the glass-roofed city below.