All were asleep, that is, but one. That brought Pemberton back to the problem of his mysterious assailant. Why had this Ganymedan tried to whiff him out of existence? Grant frowned. No one on board knew of his mission, not even the captain. On the passenger list he was merely Dirk Halliday, an inconspicuous commercial traveler for Interspace Products. Yet someone had manifestly penetrated his disguise and was eager to remove him from the path of whatever deviltry was up. Who? Grant gave a little start, then swore softly. Of course! Why hadn't he thought of it before! The scene came back to him, complete in every detail, as though he were once more back on Earth, in the small, simply furnished office of the Interplanetary Secret Service. The Chief of the Service was glancing up at him keenly. Beside him was a tall, powerfully shouldered Ganymedan, Miro, Inspector for Ganymede. Grant looked at him with a faint distaste as he sat there, drumming on the arm of his chair with his spatulate fingers, his soft-suction padded hoofs curled queerly under the seat. There was something furtive, too, about the red lidless eyes that shifted with quick unwinking movements. * * * * * But then, Pemberton had small use for the entire tribe of Ganymedans. Damned pirates, that's all they were. It was not many years back since they had been the scourge of the solar system, harrying spatial commerce with their swift piratical fliers, burning and slaying for the mere lust of it. That is, until an armada of Earth space-fliers had broken their power in one great battle. The stricken corsairs were compelled to disgorge their accumulations of plunder, give up all their fliers and armament, and above all, the import of metals was forbidden them. For, strangely enough, none of the metallic elements was to be found on Ganymede. All their weapons, all their ships, were forged of metals from the other planets. It was now five years since Ganymede had been admitted once again to the Planetary League, after suitable declarations of repentance. But the prohibitions still held. And Grant placed small faith in the sincerity of the repentance. The Chief was speaking. "We've called you in--Miro and I," he said, in his usual swift, staccato manner, "because we've agreed that you are the best man in the Service to handle the mission we have in mind." Grant said nothing. "It's a particularly dangerous affair," the Chief continued. "Five great space-fliers, traveling along regular traffic routes, have all vanished within the space of a month--passengers, crews and all. Not a trace of them can be found." "No radio reports, sir?" "That's the most curious part of the whole business. Everyone of the fliers was equipped with apparatus that could have raised the entire solar system with a call for help, and yet not the tiniest whisper was heard." * * * * *