"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.
Before dawn, El Tigre looked like a military encampment. In the glare of great searchlights, men were digging trenches, leveling a landing field for the planes, and planting the battery. The Doctor had his ray machine ready for use.