Much of a mystery was made of it. Police had failed to identify three of the four red-uniformed corpses left behind. Fingerprints identified the other as a noted criminal recently out of Leavenworth.
No one seemed to have any idea why the thorium had been taken, since the chief use of that radioactive metal, which is similar to radium, but far less active, is in the manufacture of gas mantles.
It was farther stated that the raiders had released "clouds of a luminous purple gas," which had caused most of the fatalities, and which seemed to have destroyed the gravity of metallic objects about. It was said that the factory building was curiously wrecked, as if the heavy machinery had gone up through the roof.
At first it struck me that this must be simply a newspaper canard. Then I remembered what Bill Johnson had told me of the strange red airplanes in Durango, and of the mystery of the secret radio station. Then I was not so sure. I ate a little breakfast and hurried out to the landing field. I found Bill with a copy of the paper in his hand. His wrinkled face had a look of eager concentration on it.
"Howdy, Bob," he drawled. "This looks interesting. Have you seen it?" I nodded. "It must be the same red planes. Let's get off."
We walked out on the field, where the "Camel-back" plane was waiting. It was the first one I had seen; one of the first models built, I believe. It was based on Cierva's Autogiro, or "windmill plane". But there was an arrangement by which the rotating mast could be drawn into the fuselage, the rotation stopped, and the vanes folded to the side, so that the machine, in the air, could be transformed into an ordinary monoplane, capable of a much higher flying speed than the Autogiro. When the pilot desired, a touch of a button would release the mast and vanes, and the machine became an Autogiro, which could spiral slowly or drop almost perpendicularly to a safe landing on a small spot of ground.
The machine had a further innovation in the shape of a Wright turbine motor. This had but a single important moving part, the shaft which bore the rotors, the flanged wheel that drew the mixture into the combustion chamber, and the propeller. Because of its extreme light weight and high efficiency, the internal combustion turbine engine now promises to come into general use.
The name of the machine, "the Camel-back," was due to the peculiar hump to the rear of the mast, covering the levers for raising and lowering the rotating "windmill."
The plane carried a .50 calibre machine gun in the forward cockpit.
"Get aboard, Bob, and we're off," Bill said as we got on our parachutes. "The tramp weighed anchor at four this morning, and the destroyers left an hour later. We'll be able to pick them up."