"The Second Shell" follows Robert "Tiger Bob" Barrett, a San Francisco newspaperman recruited late one night by veteran Secret Service agent Bill Johnson for a mission to Mexico. Johnson has been staying at El Tigre, a gold-and-thorium mine in Durango owned by Barrett's old college acquaintance Dr. Vernon and his daughter Ellen. Strange radio signals—chirps and squeals unlike any human voice—have been traced to Mocolynatal, a remote volcanic peak near the mine, along with sightings of stubby-winged red airplanes and Japanese tramp steamers running mysterious cargo along the coast. Barrett agrees to join Johnson, flying south in an experimental autogiro-monoplane hybrid called the Camel-back. Before they depart, news breaks that red airplanes have raided a thorium factory in St. Louis, killing hundreds and releasing a luminous purple gas that seems to destroy the weight of metal objects. Barrett and Johnson fly out to rendezvous with two Navy destroyers shadowing a suspect tramp steamer. At dawn, red planes attack the ships with the same gravity-negating gas bombs, sending men, guns, and eventually the entire destroyer floating helplessly into the sky. Barrett escapes by parachute and is rescued from the sea by Johnson in the Camel-back. The two fly on to El Tigre, reuniting with Dr. Vernon and Ellen, now grown into a striking, capable young woman. Vernon reveals he has perfected the "Vernon Ray," a controllable radiation weapon derived from an artificial thorium alloy, Vernonite, capable of killing or destroying matter at a distance. That day, a red plane lands and out steps Herman Vars, a disfigured former acquaintance of Ellen's from university, now clad in a garish uniform and claiming allegiance with beings from beyond the sky. Vars announces he knows of Vernon's death ray and Vernon's stolen blueprints (smuggled out by a treacherous former assistant, Pablo) and that he will return the next day to seize the mine's thorium stores. As his plane departs, Barrett glimpses its true pilot: not a man, but a tentacled, luminous purple creature. Johnson rushes to Durango and returns with Mexican government troops, artillery, tanks, and aircraft to defend the mine. At dawn Vars's red fleet attacks, dropping gravity-destroying bombs that send soldiers, vehicles, and even Vernon's death-ray apparatus hurtling into the sky. Barrett, aloft in the Camel-back, is caught by the gas and drifts toward the edge of space before drifting back down half-frozen. He returns to find the mine devastated and Ellen, Vernon, and Johnson missing, presumably taken captive. Flying to Mocolynatal, Barrett discovers the volcano's crater houses a hidden base: a lit array of red-metal buildings, a landing field of red planes, and a lake of seaplanes—Vars's staging ground for world conquest. Sneaking in, Barrett is captured and imprisoned, glimpsing one of the purple, tentacled alien beings up close. The next morning he is placed aboard a red plane that climbs vertically, far above the atmosphere, revealing an astonishing discovery: the top of Earth's air has frozen into a second, transparent crust—a vast purple world of solid gas, mountains, deserts, and a scarlet metal city, populated by luminous octopus-like beings with whom the insane Vars has allied himself, promising them conquest of the surface world in exchange for their power. Aboard the flagship above this alien city, Barrett is reunited (violently) with his captors' intentions: Vars boasts of world-conquest plans and reveals he possesses Vernon's ray technology, both mounted on his ships and installed in the alien city itself. Barrett secretly uses a smuggled pocket-sized version of the Vernon Ray, given to him earlier, to irradiate Vars's men, inducing a slow, lethal chemical poisoning in their blood. In the chaos—compounded by an attack from one of the tentacled alien beings—Vars's guards collapse dead or dying. Barrett is reunited with Ellen, Bill, and Dr. Vernon, who had been held captive, and the four escape aboard the enemy ship. As they flee across the frozen purple landscape, the alien city's own ray-weapon dome swings to fire on them. But Dr. Vernon reveals that the stolen blueprints he allowed to be copied were subtly, deliberately flawed—rigged to cause a catastrophic atomic explosion of the molten Vernonite core. The alien city's weapon detonates in a blinding flash, annihilating the entire scarlet metropolis in the sky. A year later, Barrett and Ellen are married, and Dr. Vernon continues studying the captured alien ship and refining his ray technology. The story closes with the surviving quartet planning a return expedition into the "Second Shell"—the frozen upper atmosphere—to learn whether other alien cities or civilizations remain in that hidden world above the air, and whether they hold promise of peaceful exchange or renewed threat to Earth.
By Jack Williamson · First published 1929 · Genre: Science Fiction, Pulp Fiction, Adventure · 4 chapters