he plane accepted the challenge and bore down at full speed on the stranger. Again came a puff of smoke, but the plane swerved and an answering shot came from its side. It was above the helicopter, and the shell which missed its mark plunged to the ground. When it struck there came a roar and a flash and the whole earth seemed to shake. The helicopter shot upward into the air and forward, both its elevating fans and its propellers whirling blurs of light. The airplane followed at its sharpest climbing angle, but was helpless to compete with its swifter climbing rival.
"He's got away!" groaned Carnes.
"Not yet, old dear!" cried the Doctor hopping with excitement. "He isn't safe yet. I never told you, but one Breslau gun had been made and it is on that plane. It has deadly accuracy and is good for fifteen miles. That's Lieutenant Dreen at the controls and Mason at the gun."
As he spoke the plane swung around and made a half loop. For a few yards it flew upside down and then whirled swiftly. As it turned there came a sharp report and a puff of smoke from its rear cockpit. High above, the helicopter had ceased climbing and hovered motionless. As the plane fired, the helicopter shot forward like an arrow from a bow, and thereby spelled its doom. Not for nothing did Captain Mason bear the title of the best aerial gunner in the Air Corps. He had foreseen what the action of his opponent would be and had allowed for just such a move. Far up in the sky came a blinding flash and a cloud of smoke. When the smoke cleared the sky was empty, except for a little scattered debris falling slowly to the ground.
nd that's that!" exclaimed Dr. Bird as he finished his examination of the underground laboratory with which the gun platform connected. "The lamp has gone to glory with Breslau's gun model and two of the best brains of the Young Labor party. I am sure that Stanesky was one of those two men. I wish the whole gang had been on board."
"Don't you think that this is the end of it, Doctor?" asked Carnes.