"Very well; Luhor will explain later what you're here for. Meanwhile you are free to go anywhere you like within the city, but be ready to work about eight earth-hours from now." As abruptly as she had come, Commander Cynthia Marnik turned and was gone. The men smoked and talked among themselves, speculating what their tasks might be. The memory of the Prison Swamp was too recent for them to care much. Mark rose quietly and stepped out of the dining-room. He'd noticed that Aladdo was absent from the meal, and he wondered if his Venusian friend was still an 'honored guest.' Deciding to inspect the city, Mark tried to retrace his steps to those buildings where he had heard the blast furnaces; but at the first cross-corridor Ernest Carston stepped out and walked beside him. He smiled at Mark Denning, but held a warning finger to his lips. They walked in silence, while the corridors became rockier and more dimly lighted. At last, far away from the city, Carston stopped under an immense jutting rock and quietly gripped Mark's hand. There was a world of feeling in his voice as he said barely whispering: "I'd lost hope of ever seeing any of you again!" "How did you get here?" Mark asked the question that had been burning in his mind. "Did they pick you up at the swamp, too?" "Yes. We're both on the same trail--and here the trail ends." "But I had no idea you'd preceded me," Mark told him. "It must have been considered a far more important assignment than I was told, to send _you_ to the Swamp!" "We didn't know, we weren't certain," Carston said thoughtfully. "But we received a bit of information which, if true, was of the greatest importance. It seemed impossible, fantastic, but the hazard was so great, that even what amounted to a vague rumor warranted my going. You were to follow in a few months, without knowing I had gone ahead. Well, you already know most of the rest; but Earth's government doesn't even suspect the deadly peril it will soon have to face!" "I'm afraid," Mark stated frankly, "that there are a lot of gaps in what I do know. I can tell, of course, that something mighty big is going on here. But what was that bit of information you received?" "It goes back nearly a quarter of a century," Carston replied slowly, "and concerns a man named George Marnik. He, and his young wife, were among the first pioneers to venture out to Callisto. Those were the ruthless years, when the great Earth Monopolies stopped at nothing, were very often lawless, and usually got what they wanted." Carston paused to light a cigarette. * * * * *