As it rose, I glimpsed the pilot of the machine. It was not a man! It was a queer, gleaming purple shape, with many tentacles! With strange horror grasping at my heart, I looked quickly at the others, but it seemed that they had not seen it. Then I remembered the Doctor's words of "creatures of the upper air" and I thought of what Ellen had said of the thing that had risen from the wrecked ship. "That was Herman Vars," Ellen whispered to me. "We met him at the University. He had a warped mind--tinkered with radio and claimed he was getting in touch with beings of a plane above the earth. Then--once--" she paused, flushing a little, "--well, he came to me and told me that he was going to conquer the earth, and that he wanted me to--to go with him. That was why we left Austin. I thought he was only insane--but this!" "And he must have been t-t-t-t-telling the t-t-t-t-truth!" the Doctor said. "And he is coming after my thorium! I wonder--Pablo--the blueprints--" Suddenly he left us and ran down the hall. "Pablo Ysan was a Mexican who helped him sometimes in his experiments," Ellen told me. "He went away a month ago. He must have carried Dad's plans to Vars." The Doctor came back with a grim look on his face. "They're g-g-g-g-gone!" he said. "That's why they want thorium. And I've got enough here to wipe out the earth, if they can use it--if they can use it," and a grim half-smile flickered over his face. "I'll run down to Durango on the rail car," Bill said. "I can have a train load of troops up here by night. Mendoza is one of my _amigos_--once I did him a good turn--" The Doctor nodded. "And if anything happens while I'm gone, you have your ray, and Bob can take up the Camel-back." The Battle He went out. In a few minutes I heard the sputter of a gasoline engine, and the ringing of the little car's wheels on the rails, as it sped down the narrow track. The machine dwindled to a black speck on the desert's rim, and dropped out of sight. Dr. Vernon spent the evening tinkering with his tube. I went over with Ellen, to look at the mine. The men had been frightened by the red ships, a few days before, and had left on the train. The place was deserted. We peered down the silent black shaft, and went back. But most of the time I spent watching the sky for a sight of the red planes, ready to warn the Doctor and to go up to meet them. Four trains pulled in before midnight, carrying one of those mobile military units with which the Montoya government so effectively nipped in the bud the revolutionary movements of 1933 and 1935. There was a battery of eight French seventy-fives and a heavier railway gun, four light tanks, a dozen battle planes and two bombing planes, and about four hundred infantry.