Bell, then, was in a direct line from Rio to the source of a radio direction signal. Fifty miles back, where the big amphibian had crashed, he was in the same air line. To extend that line on into the interior would give the destination of Ribiera, and the location of the headquarters where direct communication with The Master was maintained. He worked busily. His maps were in separate sheets, and it took time to check the line from Rio. When he had finished, he computed grimly. "At a hundred miles in hour...." He was figuring the maximum distance which could plausibly be accepted as a day's journeying by air. He surveyed the maps again. "The plateau of Cuyaba, at a guess. Hm.... Fleets of aircraft could practise there and never be seen. An army could be maneuvered without being reported. Certainly the headquarters for the whole continent could be there. Striking distance of Rio, Montevideo, Buenos Aires, La Paz, and Asuncion. Five republics." * * * * * Certainly, from his figures, it seemed plausible that somewhere up on the Plateau of Cuyaba--where no rails run, no boats ply, and no telegraph line penetrates; which juts out ultimately into that unknown region where the Rio Zingu and the Tapajoz have their origins--certainly it seemed plausible that there must lie the headquarters of the whole ghastly conspiracy. There, it might be, the deadly plants from which The Master's poison was brewed were grown. There the deadly stuff was measured out and mixed with its temporary antidote.... Paula came back, a young man with her. Her eyes were wide and staring, as if she had looked upon something vastly worse than death. "He--Ribiera," she gasped. "My uncle, he owned this place. They--have him here--alive--and mad! And all the rest...." Bell fumbled in the pocket of his flying suit. The young man with Paula was looking carefully at the plane. And there was a revolver in a holster at his side. An air of grim and desperate doggedness was upon him. "This is--my cousin," gasped Paula. "He--and his wife--and--and--" * * * * * The young man took out his weapon. He fired. There was a clanging of metal, the screech of tortured steel. Bell's own revolver went off the fraction of a second too late. "You may kill me, Senhor," said the young man through stiff lips. His revolver had dropped from limp fingers. He pressed the fingers of his left hand upon the place where blood welled out, just above his right elbow. "You may kill me. But if you and my cousin Paula escaped.... I have a wife, Senhor, and my mother, and my children. Kill me if you please. It is your right. But I have seen my father go mad." Sweat, the sweat of agony and of shame, came out upon his face. "I fought him, Senhor, to save the lives of all the rest. And I have spoiled your engine, and I have already sent word that you and Paula are here. Not for my own life, but...."