The Second Shell by Jack Williamson

Reporter Robert Barrett is pulled from routine into a nightmare of secret radio signals, vanished mine shipments, and red aircraft that seem to obey no earthly power. When a thorium factory in St. Louis is devastated by a luminous purple gas that cancels gravity, Barrett and veteran operative Bill Johnson are drawn into a race across Mexico and the Pacific, using the remarkable Camel-back to chase a threat that grows more impossible by the hour. At El Tigre Mine in the Sierra Madre, Barrett meets Dr. Vernon and his daughter Ellen, whose desert isolation hides a world-changing invention: a thorium-powered beam and an atomic-energy weapon capable of wrecking matter itself. But the real danger is Herman Vars, a ruthless mastermind whose red fleet, anti-gravity bombs, and hidden crater fortress reveal a bid for conquest backed by inhuman allies from the upper air. As Barrett is captured, witnesses a glowing tentacled horror, and discovers that his companions may have been taken aboard a vast airborne stronghold, the story builds toward a clash of science, romance, and alien menace on a scale that could decide the fate of the world. This edition has been fully restored with modern typesetting, custom cover design.