"How do we know you are Sako?" said the voice at last. "Give the recognition." "The insignia of Dr. Ku Sui?" "Yes. It is----" Carse's ray-gun prodded the stomach of the sweating Sako. "An asteroid," he said hastily, "in the center of a circle of the ten planets." The unseen speaker was quiet. Evidently he was conferring with someone else, probably Ku Sui. "All right," his toneless voice came back at last. "You will remain motionless in your present position, keeping your radio receiver open for further instructions. We are approaching and will be with you in thirty minutes." Carse motioned to Friday to switch off the mike. Sako sank limply into a chair, soaked with perspiration. "Now we must wait again," the Hawk murmured, crossing his arms and scanning the visi-screen. * * * * * They had heard from Ku Sui, but that had not answered the old tormenting question of how he would come. It was more puzzling than ever. The visi-screen showed nothing, and it should have shown the Eurasian's decelerating ship even at twice thirty minutes' time away. They looked upon the same vista of Jupiter and his satellites, framed in eternal blackness; there was no characteristic steely dot of an approaching ship to give Carse the enemy's position and enable him to shape his plan of reception definitely. Twenty minutes went by. The strain the Hawk was under showed only in his pulling at the bangs of flaxen hair that covered his forehead as far as the eyebrows. He had, from Judd's words, expected a mystery in Ku Sui's approach. There was nothing to do but wait; he had made what few plans and preparations he could in advance. Friday broke the tense silence in the control cabin. "He's _got_ to be _somewhere_!" he exploded. "It isn't natural for the screen not to show nothin'! Isn't there somethin' we can do?" The Hawk was surprisingly patient. "I'm afraid not," he said. "It's invisibility he's using, or else the fourth dimension, as Judd said. But we've got one good chance. He'll send more instructions by radio, and surely, after that, his ship will appear----" A new voice, bland and unctuous, spoke in the control cabin from behind the three men. "_Not necessarily, my honored friend Carse_," it said. "_You will observe there is no need for a ship to appear._" Ku Sui had come. CHAPTER III _The Wave of a Handkerchief_ He stood smiling in the door-frame leading aft to the rear entrance port. There was all grace in his posture, in the easy angle at which one arm rested against the side bulkhead, in the casual way in which he held the ray-gun that bored straight at Carse. Height and strength he had, and a perfectly proportioned figure. Beauty, too, of face, with skin of clearest saffron, soft, sensitive mouth and ascetic cheeks. His hair was fine and black, and swept straightly back from the high narrow forehead where lived his tremendous intelligence.