Not a word was spoken when they reached the abode of their guide. They entered an elaborate hall and were whisked upward in an automatic elevator. Detis ushered them into his apartment when they alighted. He smiled gravely at their looks of wonder as they cast eyes on the maze of apparatus before them. It was a laboratory rather than a living room in which they stood. Detis led them to an adjoining room where he bid them be seated. They exchanged wondering glances as their host paced the floor vigorously before speaking further. "Friends," he finally blurted, "I hope you'll excuse my emotion but the news you brought is a terrible blow to me as to all Europa. Carli, our prince, beloved son of Cardos, was commander of the ship you reported lost. We deeply mourn his loss." * * * * * Carr and Mado waited in respectful silence while their host made effort to control his feelings. "Now," he said, after a moment, "I can talk. You have many questions to ask, I know. So have I. But first I must tell you that Carli's was an expedition to your own worlds. A grave danger hangs over them and he was sent to warn them. He has been lost. Our only space-ship capable of making the journey also is lost. Six Martian years were required to build it, so I fear the warning will never reach your people. Already the time draws near." "A grave danger?" asked Mado. "What sort of a danger?" "War! Utter destruction! Conquest by the most warlike and ambitious people in the solar system." "Not the people of Europa?" asked Carr. "Indeed not. There is another inhabited satellite of Jupiter, next farthest from the mother planet. Ganymede, you call it. It is from there that these conquerors are to set forth." "Many of them?" inquired Mado. "Two million or so. They're prepared to send an army of more than a tenth of that number on the first expedition." "A mere handful!" Carr was contemptuous. "True, but they are armed with the most terrible of weapons. Your people are utterly unprepared and, unless warned, will be driven from their cities and left in the deserts to perish of hunger and exposure. This is a real danger." "Something in it, Carr, if what he says is true. We've no arms nor warriors. Haven't had for two centuries. You know it as well as I do." "Bah! Overnight we could have a million armed and ready to fight them off." * * * * * Detis raised his hand. "You offend me," he said gravely. "I have told you this in good faith and you reward me with disbelief and boastful talk. Your enemies are more powerful than you think, and your own people utterly defenceless against them." "I'm sorry," Carr apologized, "and I'll listen to all you have to say. Surely your prince has not given his life in vain." He was ashamed before this scientist of Europa. A tinkling feminine voice from the next room called something in the Europan tongue.