Tom Swift turns his inventive genius toward astronomy, seeking a way to observe life on distant planets like Mars. He begins experimenting with a rare green substance scraped from a meteorite found in South America by his giant servant Koku. When he discovers that this element reacts to light and electricity by becoming thousands of times more transparent than plate glass, he conceives of building a space-eye lens powerful enough to pierce millions of miles of space.
However, the project immediately attracts criminal attention. Spies linked to a rival glass manufacturing firm attempt to steal Tom's formulas and sabotage his equipment, including drilling holes in his seaplane's pontoons and breaking into his secret subterranean vault. Adding to the tension, a shipment of the crucial meteorite material is accidentally jettisoned into the ocean off the coast of Cuba during a severe storm.
Undeterred, Tom enlists a veteran salvage diver named Captain Britten and sails to the Caribbean aboard a salvage barge. Working deep beneath the surface, Tom and his crew confront dangerous marine hazards, successfully recover the massive meteorite from the ocean floor, and return with a fresh supply of the unknown element designated as X.
Back in his laboratory, Tom not only refines the material for his massive telescope lens but also perfects a parallel invention: a bendable glass as flexible as rubber and as strong as steel. He successfully fends off industrial thieves who manage to temporarily infiltrate his security and steal his patent papers, recovering the documents just in time.
The narrative culminates in a major expedition to the summit of an Adirondack mountain. Transporting the gigantic thirty-five-foot green disk via a specially built truck, Tom and his associates set up the instrument above the blurring atmospheric haze of the lower altitudes. When the young inventor finally electrifies the disk and peers through the eyepiece toward Mars, he and his companions are stunned to witness detailed visions of an alien metropolis with towering buildings and active inhabitants.
