"Good landing field," said Bell, his eyes narrowing suddenly. "On the direct route. Fifty miles back there's another landing field. I wonder...." He was already suspicious before he flattened out above the house, while dogs fled madly. He noticed, too, that horses in a corral near the buildings showed no signs of fright. And horses are always afraid of landing aircraft, unless they have had much opportunity to grow accustomed to them. The little plane rolled and bumped, and gradually came to a stop. Bell inconspicuously shifted a revolver to the outer pocket of his flying suit. Figures came toward them, with a certain hesitating reluctance that changed Bell's suspicions even while it confirmed them. * * * * * "Paula," he said grimly, "this is another landing field for Ribiera's emergency use. It sticks out all over the place. Relatives or no relatives, you want to make sure of them. You understand?" Her eyes widened in a sudden startled fear. She caught her breath sharply. Then she said quietly, though her voice trembled: "I understand. Of course." She slipped out of the plane and advanced to meet the approaching figures. There were surprised, astounded exclamations: A bearded man embraced her and shouted. Women appeared and, after staring, embraced. Paula turned to wave her hand reassuringly to Bell, and vanished inside the house. Bell looked over his instruments, examined the gas in the tank, and began to work over his maps in the blaring sunlight. He cut out the switch and the motor stopped with minor hissings of compression. The maps held his attention, though he listened keenly as he worked for any signs of trouble that Paula might encounter. He was beginning to have a definite idea in his mind. Ribiera had talked to a headquarters somewhere, by beam radio from Rio. Beam wireless, of course, is nothing more or less than a concentration of a radio signal in a nearly straight line, instead of allowing it to spread about equally on all sides of the transmitting station. It makes both for secrecy and economy, since nearly all the power used at the sending apparatus is confined to an arc of about three degrees of a circle. Directed to a given receiving station, receiving outfits to one side or the other of that path are unable to listen in, and the signal is markedly stronger in the chosen path. Exactly the same process, of course, is used for radio directional signals, one of which still buzzed monotonously in Bell's ears until he impatiently turned it off. A plane in the path hears the signal. If it does not hear the signal, it is demonstrably off the straight route. * * * * *